It’s been 15 years since Michael Lewis’ “Moneyball” revolutionized baseball and became the best-selling book in the sport’s history. You don’t have to remind Billy Beane that he’s the godfather of analytics or that Brad Pitt was cast to play the A’s general manager in the movie adaptation. Beane marvels at how dated those legacies have become. Even rereading the book, he said, “is like watching an episode of ‘The Flintstones.’ ”

There’s a more immediate plot to Wednesday’s wild-card game at the Stadium and it has nothing to do with Hollywood or sabremetrics. The Yankees are about to run into a mirror image of themselves in the A’s — a home-run hitting, bullpen-reliant powerhouse that has no fear of distilling its season to nine innings on the road. Beane chuckled at his young players’ reaction after realizing the Yankees had clinched home-field advantage last week.

“They were like, ‘We’re playing in New York? Cool, it means we’re that much closer to Boston,’ ” Beane said by phone.

That swag comes straight from the top, of course, courtesy of a cutting-edge exec who’s never had anywhere near the Yankees’ wealth but has still has made it to the postseason eight times in the new millennium. Only the Bombers, Cardinals, Braves and Red Sox have had greater success.

The A’s poverty is a familiar narrative, so Beane doesn’t expect anyone to feel sorry for him. Besides, if money was that important, he would’ve taken the Red Sox’ GM job back in 2002 and pocketed a cool $12.5 million over five years. He said yes — then no. It took Beane less than 24 hours to decide he preferred family over the higher Q-rating, which he swears made for good karma all around: The Sox ended up hiring Theo Epstein and won their first World Series in 86 years in 2004.

Beane? He stayed on the coast where he often reports to work in his shorts and flip-flops and continues his long-distance rivalry with Brian Cashman — who is both a bro and industry antagonist. The relationship, as they say, is complicated.

The two talk and text throughout the season, discussing not just baseball but their families, politics and the bizarre scaffolding of their friendship. On one hand, Beane says Cashman “probably belongs in the Hall of Fame” for his 20-year run of excellence in The Bronx. On the other hand, Beane says, “that little bastard keeps notes on every conversation we have. He’ll say, ‘you told me such-and-such in 2007.’ And of course he’s right, but I’ll say, ‘Dude, I’m your friend. You’re keeping notes on ME?’”

Cashman disputes none of it.

“We’re friends, but when we speak to each other as general managers, if Billy says, ‘I can’t stand this player or ‘this player is a problem in the clubhouse,’ I take notes on that,” Cashman said. “Someday that player might be available in a trade or he might be a free agent and those are things you want to remember.”

Hearing that explanation only cements Beane’s admiration for Cashman.

“He’s a shark, swimming around with that dorsal fin just above the water level,” Beane said. “Look, Brian is one of the best who’s ever done this job and he does it without an ego. Think about it: Never negotiated his contracts in public, never threatened to leave the Yankees, even though he could’ve made more money if he used that leverage. He’s been in the shadow of [George] Steinbrenner, [Joe] Torre, [Derek] Jeter, A-Rod and yet he’s still here after all these years.”

Cashman’s response? Straight-up shark.

“Ah, come on. Billy’s just trying to set me up for an upset [in the wild-card game],” Cashman said. Not that anyone could blame Beane. He still hasn’t won a world championship despite giving birth to a generation of analytics. Beane might be a genius, but as critics say: What’s he have to show for it?

Some of it is tied to the depressed payroll, sure. That means the A’s can’t hold onto players in their primes — “We get the great players on the way up and the ones on the way down.” And then there’s October’s cruelest axiom, that the postseason’s outcomes are random and unpredictable, guaranteed to break your heart.

Beane learned that lesson in 2001, when his A’s won 102 games, had two MVPs (Jason Giambi, Miguel Tejada), a Cy Young Award winner (Barry Zito) and a 21-game winner in Mark Mulder. Beane said, “That was as talented a team as I’ve ever been around, but history won’t remember us like that because we didn’t win Game 3 [of the ALDS].”

That was the Derek Jeter Flip game; no other asterisk required. The Yankees, nearing the end of the Core Four dynasty, weren’t the better team, but they, not the A’s, went to the World Series. It was a crushing setback, but Oakland’s ability to out-perform its payroll didn’t go unnoticed.

It was about that time that Lewis, the author, approached Beane, asking to embed in the A’s front office. He wanted to write a feature for the New York Times business section. The more Lewis learned, the greater the scope of his writing. That piece eventually evolved into “Moneyball,” which has sold more than 1 million copies worldwide.

Lewis, of course, picked the right guy. Beane wasn’t just smart, he’d seen right through baseball’s stone-age practices. Remember: The game’s front offices used to be dominated by ex-players and an old-boy network that was stuck in the ’60s and ’70s.

As archaic as it was, Beane loved the game enough to turn down a football scholarship at Stanford in 1980 to instead sign with the Mets out of high school. He, along with Darryl Strawberry, was a first-round pick that year. That’s the other part of Beane’s résumé that goes unnoticed: He was a beast of an athlete; a quarterback who might’ve had a career in the NFL.

I saw that firsthand in spring training in 1985, not long after I’d started my baseball-writing career at The Post. I’d become friendly with Beane and invited him to meet one of my college buddies who happened to be in St. Petersburg at the time. His name was John Witkowski, who not only QB’d the Columbia Lions but was drafted into the NFL in ’84 and went on to play for the Detroit Lions.

The two ended up throwing a football around in a parking lot — two quarterbacks and their dueling spirals. The Mets had lured Beane away from Stanford because he was 6-foot-3 and could hit for power, but Witkowski had a second opinion on that. “I think Billy might be better than me,” he later said.

Indeed, Beane was a can’t-miss, all-around monster — or should have been. But there were a few red flags along the way. That spring he introduced me to his own BFF, a runt of a southern Californian named Lenny Dykstra. It seemed impossible that these two could be friends, but Lenny’s primal humor amused Billy. There was something irresistible about Dykstra’s competitive ethos.

“I remember we were in the dugout before a spring training game [against the Phillies] and Lenny says to me, ‘Who’s that lefty warming up?’” Beane said. “I said, ‘Are you kidding me, that’s Steve Carlton. He’s one of the greatest pitchers ever.’ Lenny couldn’t care less. He said, ‘Whatever, dude. I’ll stick him.’ And guess what — he got a base hit off him.”

Dykstra used to tell Beane he was too smart for his own good, that he was guilty of reading too much. “Bad for your eyes, Beaner,” is what he’d say. It was crazy advice except there was indeed something missing from Beane’s arsenal. The Mets gave up on Beane before the ’86 season, sending him to the Twins for Tim Teufel, although the future GM had one last moment of greatness, going 5-for-5 with four RBIs against the Yankees on April 29, 1986.

The performance looked impressive in my scorebook until I asked Don Mattingly for an evaluation.

“What did you think?”

“About Beane? He looks like he could be a model or a movie star.”

I laughed. “No, I mean as a hitter.”

Mattingly shook his head. “Too much top-spin.”

Thirty-three years later, the scout in Beane had to agree.

“I never knew [Mattingly] said that about me, but he was right,” Beane said. “My top hand was too dominant. It goes to show you that baseball isn’t just an athletic sport, it’s a skill sport. I relied too much on being a good athlete. Mattingly — he understood the strike zone. He was a great player.”

Beane’s career in the majors lasted only three more years, totaling just 301 at-bats and a .219 average. The lessons have stayed with him to this day, but so has the experience in New York, the Mets in particular. Beane isn’t ashamed to say, “I have a soft spot for them. I know how cool it is when they win; when I was there, the Mets were like the Rolling Stones.”

But that’s where Beane puts a tourniquet on the conversation: He’s not leaving the A’s to rescue the Wilpons. Not now, not ever. Hand on his heart, Beane says he’s committed to the A’s and the baseball community in Oakland as they gear up for one more October. The smartest man in baseball is hoping that, this time, his heart wins out over his brain.

Award-winning writer Bob Klapisch has covered the Yankees and Mets for The Post, Daily News, Bergen Record and USA Today. He is currently collaborating with Rolling Stone’s Paul Solotaroff on a book about the 2018 Bombers.