About a month ago, I did exactly what you are planning.
My 73 Trillium 1300 came with 14' tires when I bought it, a few yrs ago..P185 75R14 on the axle, and a 14" bias-ply tire for the spare !! I got new P tires in the same size shortly after for the running gear, using one of the originals for the spare.
After the trailer acquired a "lean" to the street side last season, I decided a new axle was in order; so, in May, I had a new axle installed:
#10 3000Lb Dexter axle w/10inch brakes
I don't know if they changed the starting angle ( 0 degrees) which the specs call for, but I now have 2 inches tire clearance in both wheel wells.
With the high capacity axle, it did not ride stiff, nor bounce on the 25 mile trip back home from the installing shop. There is NO indication whatsoever of tire contact with the wheel wells.