ipad restore has less than 1 mb of data remaining, but is hanging

I gave my iPad Air 2 to my husband, and he restored it from his older iPad. Restore worked except it won't complete -- says "This iPad is currently being restored and has less than 1 MB remaining." This has apparently been stuck for about a week -- and the iPad works fine but it won't install the latest IOS update until the restore is finished. I want to know how to complete the restore OR if I choose instead to hit "stop restoring iPad" can I first find out what app data is hanging and if it's not essential (I don't think it is).