205/75/15

op asks wrote:
I’m thinking about increasing the tire size from a 205/75/15 to 225/75/15 on a 2001 Jayco Quest.

Has anyone increased to that tire size?

Are there any benefits?

The ST205/75-15 tire takes a 5.50 wide wheel and can be a load range C at 1850 and 50 psi..... or a D at 2150 lbs capacity and 65 psi.

The ST225/75-15 tire takes a 6.00 wide wheel and can have a load range D or E at 65/80 psi respectively.

Your present wheels width and pressure rating dictate which size and load range they can use for best results.

Any recommended ST tire ply or a ST radial tire?

Would there be a difference if I used a 205/75/15 and not a ST tire?

Hmmm... a bit confusing terms but a ST comes in the old tech bias ply or a radial ply. Bias ply tires are ok on a lawn service trailer that spends its life running around town.
I would use a radial tire on a road trailer.

The 205/75-15 you mentioned IMO is a P tire and not a good idea on a trailer with 1800-2100 ?? lb minimum load requirements.

You need a ST radial on that trailer. A good upgrade would be moving on up to a LT depending on your trailers current axle ratings.