A 15000 gvwr bumper pull toy hauler is a lot of weight on the bumper as in tail wagging the dog issues. Being a tri axle will help with handling issues and hitch loads. A really big plus is three axle braking.
You have the combo so make a short trip and see how the truck handles the big bumper pull toy hauler.Then make a decision.
The only legal issues will be not exceeding the trucks steer or drive axle/tire load capacities.
And if your state has some type of weights for registration purposes.
I pull a 16k triaxle GN stock trailer with 7k axles with my '03 2500 Dodge/Cummins NV5600 tranny 3.73 gears. The truck handles the trailer beautifully even with a 16k load on the trailer and stops quicker than my 11200 lb 5th wheel rv trailer.
Having pulled that size pintle hitch trailers commercially with LDTs I would want a later model one ton drw mainly for stability and eliminating tail wagging the dog issues