If I delete and reinstall Pages will I lose my files? I have an iPad 2 running iOS 9.3.  I have many files on Pages app.  The app locks up and will not fully load all the files.  If I delete and reinstall will I lose my files?
If they are stored in iCloud Drive or another remote storage thing they will be redownloaded when you re-setup Pages. If they are not in a Cloud storage thing, they will be deleted with the app.

Since iOS 9 is a bit old at this point, newer iOS have a files app and you should be able to store all your Pages and iWork documents in file storage as opposed to storing them in the application bundle to avoid deleting any documents when you remove the Pages app.