Personally with used iphones I prefer to buy them with some sort of lengthy warranty which usually means refurbished in excellent condition. Because of that, 1 generation older iphones are sometimes not cheap enough to warrant saving the couple hundred and sacrificing any new features and new warranty, not to mention new battery. I feel that if someone is in the market for a new iphone right now, they're already willing to pay the price of the newest phone, and therefore they should go for the 16 pro/max over any savings they might have over a 15 pro/max. In my eyes there's enough upgrades/changes to hold you over for a few years without feeling like the future upgrades you don't have are starting to stack, and you feel the pressure to buy up again soon.