You will be over your GVWR of your 2500. With 20-25% of your GVWR of the 3500RL (15,500lbs) being a potential pin weight of 3,100 to 3,875 lbs, you will exceed the 2000 lb cargo weight of the 2500.
My 2006 GMC 2500 weighed 7,200 lbs with a hitch, myself and a full fuel tank. Subtract that from 9,200 lbs and that only leaves 2,000 lbs for the pin weight.
On this site and on RV.net, you will read that the GVWR doesn't mean anything. people will state that the truck GVWR doesn't really mean anything and that they use a 2500 to pull big loads. They state the GCWR of the truck as being able to handle the load. But if they don't believe the GVWR, how can they assume any accuracy in the GCWR? If one number is phony, the other one probably is also.
Most people would use a one ton or higher for the weight of the trailer.