[badpun]

Will they not release security patches to the last-supported iOS version though? I think they were doing that in the past.

[bondant]

Exactly. iOS 12 was released in 2018 and received its final security update last August. So if Apple does the same with iOS 15 we should get another 3 years of security update.

[luch]

You're absolutely right, it's still supported security wise. You just don't get the new versions of iOS

[badpun]

So, the phone will basically continue working as-is, and will still be secure. The newer versions of iOS are a mixed bag anyway. The biggest problem in practice will be the apps eventually dropping support for the old iOS version. It won't happen overnight though.