If you have bad axles then upgrading to the best tires won't help you.
A big rig trailer repair shop can tell you if anything is wrong with your trailers axles.
Then buy some quality tires such as;
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.
"good judgment comes from experience, and a lot of that comes from bad judgment" ............ Will Rogers
'03 2500 QC Dodge/Cummins HO 3.73 6 speed manual Jacobs Westach
'97 Park Avanue 28' 5er 11200 two slides