I don't think your 1500 has a #15,000 GVWR... ha, ha! That is probably your GCWR..
So, as long as your truck weighs around #5900 with everyone loaded in it and the weight of the trailers tongue weight on it and on and on, you should be fine..;) I know my truck weights at least that much with just my fat A in the truck and the other stuff I just haul around for the fun of it...
On the other hand, towing performance is different for everyone, so you just gotta decide what is your towing performance parameters? Any of us keyboard commandos can quote weight ratings and all... Just gotta decide what works for you in the end..
We ain't towing it and we ain't paying for it, so there you go.. :)
For me, you might get away with the #7500 GVWR TT, but then, what weights are you exceeding on the truck and what are you comfortable with?? I have no idea. :)
Good luck!
Mitch