My iPad keeps shutting down

Overheating is one possibility. Apple equipment shuts down if it overheats:

Keeping iPhone, iPad, and iPod touch within acceptable operating temperatures - https://support.apple.com/HT201678

Also if you are running iOS9 then realize that is an old system version. It may be trying to interact with online services that are designed to interact with newer iOS versions and you are encountering an issue where the support interface isn't working properly with an old iOS. Normally the advice would be to update the system software, except you can't with an older iPad. Another thing to check would be to see if specific apps are resulting in the shutdown. Quit all your running apps and then keep a log which ones are running so you know that if you have another shutdown. You may be able to isolate it to a particular app. If you can then you can see if you can update that app but it is very likely nobody is producing updates for anything using iOS9 now.