With the 15 you've got lots of options for a tow vehicle. There are a lot of vehicles out there with a 3500lb towing capacity, and that's enough for a 15 and another 1700lbs of stuff.
I like the 15. I suspect if the wife didn't insist on a bathroom we might have ended up with a 15a.
2013 Escape 19 ("The Dog House") , 2012 Nissan Frontier