You get a much better selection of QUALITY tires. In my opinion you would be better off with a quality LT tire, (XPS Ribbed)or with Sailun Tires.
If you have the room between the tires and also to clear your wheel wells you can go to a 16" wheel and tire. Dexter Axle tips "Tip #24: Axles should be spaced far enough apart to allow a minimum of 1" clearance between the tires. More space would be required if tire chains are to be used."
Your GVW is determined by more than just your tires. You have to take into account your axle rating, and also what the trailer frame/tongue were designed to carry.