Lack of storage space on my Galaxy s7

I have been trying to free up some space on my 32GB samsung galaxy s7( I am having to use the optimize your phone a couple of times a week just to keep my phone from telling me it is out of storage) but after deleting all my videos, most my pictures and several apps, I have only managed to get 2GB of free space. When I look at my storage, the documents, images, audio, videos and apps only total to about 13GB. Is the OS really taking up that much space? Do I need to do a reset to get that space back?

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