Your options depends on what size and load range and axle capacity and GVWR your trailer has. Never heard of a ST255/75-15 tire. IMO you mean a ST225/75-15.
Depending on room in the wheel well and proper wheel pressure/wheel width requirements the Goodyear Wrangler HT in a LT235/75-15 C (50 psi) at 1980 lb capacity. Most LT tire makers carry this size.
And a Wrangler HT in a LT215/75-15 D (65 psi) at 2090 lbs capacity.
Maxxis LT U-168 are a commercial grade tire with several 15" sizes and have became popular with all types of trailer owners.
Vanco 2 from Continental another popular tire for trailer users has several 15" sizes and load capacities.
I see the Yokohama RY215 in a 700R 15 D at 2040 lbs capacity is popular on some of the other RV websites.
Do your home work on the numbers.
Now if you have the ST225/75-15 D at 2500 lbs per tire moving up to a LT225/75-16 E at 2680 lbs capacity is the best/reliable upgrade.
