return iOS 10! on iPhone 6 ios 11 is very buggy! a lot of mistakes and crashes! Give a week for downloading through the server ios 10.x.x.! The new version is problematic for 6 models.
Not going to happen.
Apple stopped signing on iOS 10 a month, ago.
Try a hard reset of your iPad by holding down both the Home and sleep/wake buttons simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons.
In Settings app, General Reset, try Reset All Settings.
In Settings app, turn OFF Background App Refresh for any apps that don’t really need any type of web or internal data refreshing.
Additional tip, In Settings app, General, Accessibility, turn ON Reduce Motion, if you like.
Good Luck to You!