There's no way the Ford's GVWR could be 15,000 lbs. It might be the towing rating is if's a SRW, regular cab, manual transmission, 2WD, and any other stripped down option there is to save weight. But even then that sounds like a high towing rating.
My guess on the new Dodge 3500 SRW is the GVWR is around 9,900 lbs, but take that info for what it's worth (nothing).