How to get texture size down on size map

I m trying to optimize texture sizes to improve loading and such. I have a 2k texture which has a resource size of 2.7mb in the texture editor menu but 18.4mb in the size map. I dont know which to trust since they re so drastically different but would like to get the size down on the size map so i can use it to track down size issues effectivly. Any one know whats going on with this discrepency?

One is the compressed size, no?..

Did you ever get the figured out? I have a 4K tecture but told it to never do above 1024 but it still show up as large in the Map.