iPhone 6 Plus update

Sorry misread that earlier, you have a 6 Plus, which is the bigger version but not the one with a better chip. Therefore you are stuck to iOS 12. The 6s or 6s+ can be compatible with iOS 15. If you'd like to move up iOS and you're currently are using the 6+ as a main device, I'd recommend upgrading.

Sincerely,

Gray

The iPhone 6 can’t update to iOS 15., plus or not.

The iPhone 6S and 6S plus can.

Because it’s old and doesn’t have enough RAM.

How much Storage do you have right now? It should continue its update until iOS 15. If it stops at 12, can you confirm you have the plus version? Verify this in Settings > General > About > Software Version.

Thanks,

Gray

Sorry, misread that. He has a plus, not a S.