15.0 please help me us update

The iPhone 6 Plus can only go as far as iOS 12.5.7. That is the end of the update road for the iPhone 6 Plus.

It is impossible to install iOS 15 on the iPhone 6 Plus.

You need an iPhone 7 to run iOS 15. To run iOS 16, you will need an iPhone 8 or higher model.

An iPhone 6 Plus cannot be updated past iOS 12. You need a newer phone.