Iphone 14 security update life?

Thinking of getting wife an Iphone. Im not really a phone guy and particularly with new Iphones at 40k + and Thais inherent lack of care with same....aka broken screen first 3 months, lost etc... not prepared to invest money like that, Used Iphone 14, 15 seem to go between 12 - 15k and that would be acceptable to me should she get a few decent years out of it. I am specifically after an Iphone. She has an Android now and shes not into games or will get the benefit of an expensive camera so another Android, even a high end one wont be anything spesh for her.

I would be looking for an Iphone with low battery recharge cycle count and in perfect condition. I know these phones way surpass Android brands in quality and general working life but my main concern are security updates for banking apps etc. Once these stops the phone pretty much unuseable (or is it?). Apple quote 5-7 years....and for an Iphone 14 pro release date 2022, would mean min life 2027, max 2029. Do I have all this right or? 12-15k for a year or 2 doesn't sound like a good deal. ANy help appreciated