There are no 15" LT tires anymore that can meet a load D at 2540 lbs or a E at 2830 lbs capacity.
My 1997 11400 lb 5th wheel trailer came with the same ST225/75-15 D tires on 5200 lb axles. I sold the wheels and tires on CL to a guy with a lawn service trailer and went to a BFG Commercial T/A LT215/85-16 E at 2680 lbs capacity on 16" steel trailer wheels. Ran two sets for 51k and 55k miles and around 35k on the 3rd set of commercial grade all steel carcass Bridgestone R-250 with no issues. The R-250 have been replaced with the R-238...still the same all steel ply carcass tire that Bridgestone recommends for trailer service.
If you stick with a ST tire be aware with only 8 or 9/32nds of tread depth we don't get 40k-60k miles of service like a LT tire with thicker tread depth. Which most rvers never see more than 15k-20k miles before the tire times out.
The Goodyear Endurance....Carlisle HD ST tires both on the market for 3 years or so have been popular with very few if any complaints. Both are the new gen higher L and M speed rated tires.
I like the Provider ST tires from Taskmaster. They first came on commercial trailers in the '10 era and are one of the first higher speed rated ST tires.
Maxxis has been left behind still rated at 65 mph. With over 30 member reporting issues with them I would stick with a more modern brand ST class tire.