I suggest you to reset your iPad 2 and restore it then. It would reclaim much free space.
1. Please back up your iPad 2 data to iTunes first.
2. On your iPad 2, go to "Settings > General > Reset > Erase All Content and Settings" to reset your iPad 2 to factory default.
3. Go back to iTunes and restore your backup.
It may takes you much time. Please wait patiently.
Or you can also consider some third-party cache cleaner to clean your iPhone if you never cleaned your iPad 2 before. Like iMyFone iPhone Cleaner, you can google for it. It is developed to remove useless data and files from iPhone, like app cache, corrupted files, crash log, storage useless file, and more. It is free, you can have a try.