In Europe we generally make 6 years or more with tires on Travel-trailers. Safety first, but the environment is also impotant ( in Europe, mayby not in America
).
We use C( omercial) tires, the equivalent of LT .
I am convinced, that if you keep pressure to the upper border, where yust no screws tremble loose, also ST tires can last that long, and wont give tiredamage issues.
If you give GVWR of your TT , tirespecifications already given,( E load 225/75R 15), I can calculate that highest pressure for you, probably about 70 psi.