Fifteen years after 9/11, downtown is eating the terrorists’ lunch.

And drinking it, too: The mortally shattered neighborhood has rebounded with booze-fueled gusto. The area has improbably blossomed into a river-to-river mosaic of fancy hotels, restaurants headed by celebrity chefs, Madison Avenue-level stores, sparkling new parks and (soon) the city’s swankiest movie theaters.

On this 15th anniversary of the atrocity, which many believed would finish off lower Manhattan for good, the good times roll in every corner.

The zone around the World Trade Center is Ground Zero — for wining, dining and shopping. Selfie-snapping hordes make the enormous outdoor memorial pools, emblazoned with the names of the dead, seem more celebratory than solemn.

The party rages from indoor-outdoor Industry Kitchen cafe on the East River to alfresco heaven Beaubourg bistro on the Hudson. Even on Water Street’s corridor of charmless office buildings, the Dead Rabbit saloon has earned the title of “World’s Best Bar” from the Tales of the Cocktail Spirited Awards, the “Oscars of the spirits industry.”

As a real-estate columnist still guilt-ridden over being marooned in Europe on 9/11 and for a week after, I’ve long advocated in these pages for a fully revivified, commercially healthy downtown. Yet, the triumph of life over despair seems so exuberant, I sometimes wonder: can “hallowed ground” stand so much merry-making?

Does the annual reading of victims’ names give us license to party?

Of course 9/11 shattered not only downtown, but the whole city and the nation. Victims hailed from around the world. Even so, it was the few square miles at Manhattan’s southern tip that suffered worst.

Remarkably, the district has more than “recovered” from the attack that wiped out 14 million square feet of office space, chased companies uptown and to New Jersey, closed subway stations and left blocks all around in ruins.

Sidewalks teem with families and pregnant moms. The just-completed, $500 million conversion of Art Deco skyscraper 70 Pine St. from vacant offices to filled apartments awakened many sleepy, narrow and dark blocks in Fidi’s historic heart.

Many of my friends who neither work nor live in the area have no idea what it’s like today. For them, memories of the blackened hulks of the old Deutsche Bank building at 130 Liberty St. and Manhattan Community College’s old Fiterman Hall remain defining images.

The World Trade Center, too, lay in ruins for too long. Normally indomitable real-estate executives wore faces haunted by the loss of friends and colleagues. I descended into the muddy crater and saw almost nothing going on four years after the attack. A politically contrived, phony “cornerstone” laying for the Freedom Tower in 2004 was a mockery of real progress.

As recently as six years ago, One World Trade Center was little more than a slow-rising steel stump. Neither 3 nor 4 WTC was even started. The possibility that the 16-acre site would remain an empty pit indefinitely seemed all too real.

Yet, piece by piece, block by block, the rest of downtown was slowly clawing its way back with welcome grace notes.

Stone Street, once known as the “crack alley of Wall Street,” became a crowd-pleasing, European-style dining corridor. A new, glass-wrapped Staten Island Ferry Terminal banished memories of its squalid predecessor. The city built an East River Esplanade and a splendid new public pier. The hulking office tower 55 Water St. sprouted an “elevated acre” — a landscaped meadow three floors above ground.

Today, One and 4 World Trade Center, and nearly finished 3 WTC, confidently reclaim the skyline. The new and elegant 7 World Trade across the street is one of Manhattan’s most coveted office addresses. The neighborhood’s 62,000-strong residents can, on some days, seem outnumbered by tourists looking for the Statue of Liberty in the East River.

‘Piece by piece, block by block, the rest of downtown was slowly clawing its way back with welcome grace notes.’

So much vibrancy can make the drawn-out, enervating strife among elected officials, public agencies, developer Larry Silverstein, architects, insurers and victims’ families seem like a quaint memory.

Sure, much remains to be done. The World Trade Center is still waiting for one of its planned quartet of towers. Until a tenant comes along to justify its cost, the barren site is as awkward as a missing tooth.

But does anyone remember defeatist proposals to use the entire 16 acres for a memorial?

Or Donald Trump’s sour-grapes warning (after his notion to rebuild the Twin Towers one foot taller than the originals gained no traction) that the 1,776-foot-tall Freedom Tower was “terrorist target No. 1 with a bull’s-eye around its neck”?

Today’s sexy, life-affirming downtown pokes a sweet thumb in the terrorists’ eyes.

Data compiled by the Downtown Alliance business improvement district sketch a brave new world. The population, around 25,000 just before 9/11, will reach 70,000 in five years. There are 29 hotels compared with six in 2001. A thriving office market larger than most entire American cities was once Wall Street-dominated; now it boasts chemistry-changing media and fashion companies including Condé Nast, Time Inc., Omnicom, Droga5, SNY, Hudson’s Bay Company, HarperCollins, Revlon, Gucci and Hugo Boss Fashions Inc.

Some $30 billion in public and private investment after 9/11 lent muscle to the miracle. But ordinary people from around America — and from around New York — provided the heart.

They voted with their feet, moving downtown or choosing to remain there despite miserable street conditions, predictions of long-term decay and fears of another attack. The stabilizing effect of committed residents gave companies such as WOR Radio and ABN Amro, both previously in Midtown, the confidence to relocate downtown.

Among those who stood their ground right after the attacks was arts and entertainment historian, Stephen M. Silverman, a former New York Post reporter, whose latest book is the critically acclaimed “The Catskills: Its History and How It Changed America” (Knopf).

Silverman personifies the steadfast spirit that saved lower Manhattan. Yet, like some others who’ve lived through the changes, he’s ambivalent about rampant commercialization.

He moved from uptown to Beaver Street in 1998 and lived there happily until 9/11. His building emerged caked in soot from the whirlwind of smoke and ash. He has anguished memories of “Cantor Fitzgerald documents blown onto my roof deck, along with airplane parts and other flying debris.”

He and his dog spent the night elsewhere, “but we forced our way back through barricades the next day,” he recalled. Then he “hunkered down.”

He turned a broken seat from one of the hijacked jets over to the FBI “in exchange for their letting my dog run in fenced-off Battery Park.”

While he appreciates improvements since then — gourmet supermarkets! The High Line-like Liberty Park! — he acknowledges a certain sense of loss as well. “Gone is the greengrocer who opened a house account for me because with phone wires down through September 2001, credit cards couldn’t be approved. In his place now: Hermes, Tiffany and soon Saks,” he said.

For sure, downtown can seem too happy. The slayground-to-playground transformation appears as carefree as if 9/11 had occurred not 15, but 100 years ago.

Next year, beloved Tribeca restaurant Nobu will pick up stakes for 195 Broadway at Fulton Street. The buzzed-over new Beekman Hotel opens this month with restaurants from Balathazar creator Keith McNally and super-chef Tom Colicchio.

The South Street Seaport will bring Jean-Georges Vongerichten and David Chang to Pier 17. At the super-luxury iPic cinema complex to open in the Fulton Market building on Oct. 7, waitresses in chic black dresses will serve filmgoers “curated” food and wine at their seats.

More than 100 pricey stores cleave a path through and around the massacre site’s tragic heart. Saks Fifth Avenue will open in a few weeks at Brookfield Place, the former World Financial Center that narrowly survived 9/11. The Winter Garden had to be reassembled shard by shard; today it anchors a sea of boutiques and food courts.

Brookfield’s complex is linked underground to the Port Authority’s cyclopean World Trade Center Transportation Hub, much of which is a Westfield-run shopping mall.

Arguments about architect Santiago Calatrava’s stegosaurus-like Oculus — is it a masterpiece or a $4.2 billion boondoggle? — give way to more mundane issues. Do I drop by Apple before or after choosing between shirts at Turnbull & Asser and Charles Tyrwhitt?

But again, the insistent question barges in: Doesn’t the slaughter of 2,606 human beings at al Qaeda’s hands deserve a higher form of remembrance and contemplation than a shopping spree or a bar crawl?

In fact, there is a shrine to our lost souls that blows away lingering unease that maybe we’ve forgotten 9/11 too soon. That of course is the National September 11 Memorial & Museum, which opened in May 2014.

An anguish-inducing but humane engine of catharsis, it unflinchingly evokes the indelible horror — and no small amount of heroism — of that incongruously sunlit day.

Its contained subterranean confines, deeper than the memorial pools, enjoin on us a hell from which there is no escape. It is so agonizing to witness, almost unbearably so, that it atones for all the above-ground pleasure-taking.

Boxes of tissues are on hand for good reason. Everyone will be affected differently by artifacts such as bloodied shoes, wrecked fire trucks and singed driver’s licenses and lunch orders.

For me, the most awful sight might be photos of victims in the act of jumping or poised to jump from the burning towers. In a remembrance mounted nearby, a witness relates that one young woman, facing eternity, modestly held her skirt down against the wind.

Two years ago, I denounced a plan to open a cafe inside the museum where wine and beer would be served. “A bar and grill by any name on top of burnt fire trucks and human ashes is just plain gross,” I wrote.

The powers-that-be wisely dropped the idea. My griping might seem moot today.

We can sip fine Italian nebbiolo at Eataly from window tables directly over the memorial pools.

“Everybody had wine glasses in their hands,” marveled a friend who visited Eataly and its French counterpart, Le District, at Brookfield Place.

Maybe there’s nothing wrong with that after all. The museum — alcohol-free and blessedly free of “interpretation” — provides all the sobriety we need to honor the innocents we lost and to cherish their memory.

In a Nov. 16, 2001, edition of the New York Post which commemorated the newspaper’s 200th anniversary, I wrote, “One day terror will be vanquished.” I predicted that “a new icon of the harbor” where Post founder Alexander Hamilton first made landfall would soon rise where the Twin Towers stood.

We have a way to go to conquer terrorism. And for all the progress made, the new World Trade Center isn’t quite finished. But already, we can claim a finer victory than “iconic” skyscrapers — the beating, human heart of a city that wouldn’t take defeat for an answer.