It's closer to 16k than 15k gross. Dually because of the pin weight, Diesel due to the total weight.
My gas dually is right at the limits for my 13,500 gross 5er. My loaded pin weight is just a bit over what you dry pin specs state (2270 shipping pin weight). I easily have another 1,000 lbs in the bed so close to what your pin will be. The weight is no problem with my dually, load capacity of 5,000 lbs plus. My gasser's tow specs top out near 13,500 lbs with the 4.10 rear end.
Bottom line get the diesel dually and be safe and happy.