Why can't I update my iPhone 6s to iOS 15?

The iPhone 6s has reached the end of the update road. No more updates will be available for that model if you have already installed iOS 15.8.3.

If you have apps that require a higher iOS version like iOS 18.....you will need a new iPhone.

Bob Timmons wrote:

The iPhone 6s has reached the end of the update road. No more updates will be available for that model if you have already installed iOS 15.8.3.

If you have apps that require a higher iOS version like iOS 18.....you will need a new iPhone.

Unless I missed something, they seem to only want to go to iOS 15 and didn't ask about anything higher. This is why I asked what model phone they actually own. We've seen many believe they have a 6s, when they really have a 6. Hopefully, they'll come back.

Open the Settings app, then General, then About and report back what the model number of your iPhone is. While you're there, what is the current iOS version running on your iPhone.

Yes, hopefully the OP will provide more information to clarify things. Your guess may be better than mine.

If this is actually an iPhone 6 – and not an iPhone 6s – iOS 12 is the end of the line.