Toy Haulers normally have a heavy pin. This is to offset the wt of toys behind the axles. A toy hauler often has a built in generator, plus large fresh water tank. Many will have on board fuel tank.
Look at your tires. Are the rears rated to 7,000 combined, maybe 7,500? If you add suspension support, for the springs, to level the truck, the limit will still be tires/wheels.
Like I said, a TH loaded to an actual wt of 14K will be close to limit. Will it break, fall apart towing a 15K TH? Probably not. A 3500 SRW not much better (likely same tires/wheels), so a DRW would be next step.
Jerry