I had a 7 plus, now a X. Mrs has a 7 plus.
Glad to hear your not having issues.
Makes me think that they make IOS slow on the iphone 6 for a reason to try and get people to upgrade their phones and then stops people rolling back to a older version of ios.
its a shame really, all I use my iphone 6 for is text messages, calls and whatsapp so doesn't get used for much and my son will play Pokemon Go on it t times if out and he is bored or needs entertaining