I do experience lagging even on basic stuff like writing SMS or other-text inputs... (waiting 2-3 seconds for the soft keyboard to response). I'l have to do some Option->Reset when I find time... [iPhone 6+] Not good when you can't trust the device... once my iphone freezed for X seconds, then I realized that random social post were posted to FB, while I tried to touch the display... :) And that scares me :) I have to give a try to the "Reset" options :)
I own an iphone 6+ too, this could also be a hardware issue. It started for me with the touchscreen going unresponsive for a few seconds and then suddenly 'catching up', it got progressively worse so I got it repaired. Hopefully it's purely a software issue in your case but just in case : https://www.apple.com/support/iphone6plus-multitouch/
Experienced the same issue, please have a look at Privacy->Analytics. If you (like me) find a lot of errors related to mediaserverd, then 'reset network settings' will likely fix it (like it fixed the lag on my 6S after upgrading to iOS 11).
I don't experience input lag, but I definitely experience general UI lag. Everything is so jittery compared to iOS 10. Swipes, transitions, everything lags.
