You don't need a DRW truck for a trailer that size unless you just want one. However lets look at some of numbers.
Fleet Ford Body advisory spec sheets show a F250 4x4 crew cab 6.2 smallblock has a 10k and a 6100 RAWR. The F250 comes from Ford with with a 6100 RAWR and weighs a unladin 2850 lbs. Which leaves around 3200 lbs for a max axle payload. Add another 150-200 lb for a hitch and another 200 for gear and folks leaves the truck with 2800 for a wet pin weight.
The 297se Raptor web shows a 11000 ship and a 4397 CCC = a 15400 GVWR. The pin weight from a 15k 5th wheel trailer will be in the 3000 lb range.
The F250 simply doesn't have the rear suspension to handle a 5er's pin weight that size.
I don't think you will like the towing performance from the 6.2 smallblock gas engine towing a 15K trailer. I've seen towing complaints in windy areas and the hills/mountains and poor mpgs from some smallblocks gas owners that are pulling 10k-11k.
I would look at the 6.7 diesel and the F350 SRW with 11500 GVWR and especially those bigger 7000 RAWR. With up to 4500 lbs payload, This truck fits a 15k trailer requirements very well.