Storage

Deleted the iOS 12.1.1 update.

You can't install it anyways because you have little to no room left on your iPad.

You'll regain 1.53 GBs of internal storage.

Then 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.

I am not sure that storage indicator is even reading the correct amount as a 16 GBs iDevice should be reading well under that 15.6 GB number for actual total free storage space.

A 16 GBs iDevice should be reading, if full, somewhere in the 13-14 GBs range and no where near 15 GBs.

Something is computing wrong because iOS has no sufficient internal free space to operate in.

Deleting that iOS 12.1.1 update would free up more room and a hard reset might restore enough space back to your iPad so iOS is running as it should.

Not sure if the hard reset will release any more free data storage space or not, but it is always worth a try.

Go to general settings. The check iPad storage. You will see a list of what is using up your storage. Ta

No,

Go into Settings app, General, iPad Storage, wait for a list to generate.

That list will tell you exactly what is taking up all of your iPad storage space.

You can get delete the iOS 12.1.1 that will save you 1.5gb My iPad has 32hb used for system and is not deletable. Ta

Did you try the hard reset?

Next step

Backup and restore using iTunes on a computer.