"Thanks for the explanation, but ya made up the 8klb towing capacity thing."
This^^^^The OPs truck has a GVWR of 7K, and a GCWR of 15K, but his truck does not weigh anywhere near 7K as it left the factory. For example, if his truck has a payload sticker on the door jam stating not to exceed 1500 lbs, would mean it weighed 5500, when it left the factory. So for example, the OP has added 500 lbs of stuff, would be a curb wt of 6K, allowing another 9K, actually 9400 stated, before reaching the GCWR of 15K.
So while many ratings will be close, the only real concern, safety wise is the factory receiver, that can be replaced. Of course the operators experience/ability towing a large trailer is always a concern, even with a more capable truck.
Jerry