I'm on a 6S and I agree. Ive had a 4S and 5S in the past, and taken part in various beta versions of iOS.
This is the first one where performance has been massively poor for most of the beta. Of course betas are usually buggy, but this time its exceptional.
Even now on the GM, my iPhone 6S hangs on keyboard often, regular apps freeze unlike they ever have before, and battery life is unbelievably bad.
When in battery saving mode, it's essentially unusable. The SETTINGS app freezes when performing simple tasks like turning on and off Data, or Personal Hotspot, or even the Battery Saver option itself!
I'm hoping much of these stuff is addressed in subsequent patches shortly after release. The 6S is a very powerful device. There is no excuse for rubbish performance in the Settings app fro crying out loud.