Every two years, Apple redesigns the iPhone. And in between each new design is an "S" model, one that looks basically the same as the previous version but overhauls the insides to keep things fresh. 2015 is an S year.

New designs typically generate the bigger buzz since it's easier to convince people that something is worth an upgrade when it looks and feels new. But to its credit, Apple is careful to make these less-buzzworthy S refreshes about more than just adding speed or bumping up the camera. The iPhone 4S added Siri. The iPhone 5S brought TouchID and 64-bit support. And the iPhone 6S and 6S Plus are mostly about the pressure-sensitive screen, dubbed “3D Touch.”

Still, the right iPhone upgrade interval for most people continues to be once every other year or so. There’s nothing in the iPhone 6S and 6S Plus that you absolutely need if you’re already using a 6 or 6 Plus and those transformative, bigger screens. But if you’re an iPhone 5S owner looking to upgrade, the 6S and 6S Plus offer some nice stuff that wasn’t available last year. Even if you’re waiting around for next year’s hypothetical iPhone 7, you’ll have some cool features in store for you on top of whatever innovations that phone ushers in.

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Listing image by Andrew Cunningham