can iphone 6 plus update 14.7 version?

Hello. The maximum iOS version that the iPhone 6 Plus can run is iOS 12.5.4. This device cannot upgrade to a newer iOS version. If you would like to run a newer version of iOS, such as iOS 15, you will need to upgrade to a newer iPhone.

No. iOS 12.5.4 is the highest possible for that model.

No. Your over 7 year old phone is too underpowered and lacks the hardware required to run anything higher than iOS 12.5.4.