Droid Turbo 2 storage doesn't clear

We often get out of storage messages on our Motorola Droid Turbo 2 phone. We delete an App, and, say it's a 100 MB app, we only see about 10 MB free up. Likewise we've transferred and deleted gigabytes of pictures and videos from the phone, but only a tiny amount of space gets freed up. We're deleting and deleting and deleting, but we still have no room. Right now, looking at "Internal shared storage" - It shows 23.27 GB used of 24.06 GB but only 5.06 GB used for Apps and 7.32 GB used for imaged, 18.73 MB for videos, 0 for Audio, 475 MB for other and only 1.34 MB for cached data (so it's not cached data). Those don't add up to anywhere near 23.27 GB! Apps and Images numbers go down as we delete, but the total GB used barely moves! What is happening? How can we get our storage back? Per Robert's comment, we downloaded Disk Info, screen shot below. But, all it did was show that we used most of the "Data". There's no insight as to what is using it, or why as soon as we delete apps, photos, and videos, most of the amount we just freed appears to be instantly taken back up.