Q: iOS 9.3.2 iPad runs slow and almost unusable

Unfortunately you cannot uninstall an upgrade. Try a Forced Restart. Hold down the Home and Wake/Sleep buttons at the same time for about 15-20 seconds until the Apple logo appears. You will not lose anything.

These steps may help:   http://www.macworld.co.uk/how-to/ipad/how-speed-up-ipad-tips-3632709/

Also you could try a System Restore if the above does not help.

https://support.apple.com/en-us/HT201252