There is only 4 1/2" of wheel well clearance from top of tire so changing to 16" wheels won't work.
Thats a lot of top clearance for a std leaf spring trailer suspension. My current 5th wheel trailer/5200 ln leaf spring axles, has 2 3/4" to 3" top of tire clearance.
Also every 5th wheel rv trailer I've owned (3) had 5"-6" of clearance which was plenty unless your boon dockin in the back country.
2" out of level front to rear in 30' isn't much. I would make a couple of trips and then I would decide if any leveling or changes in the trailer front to rear attitude needs help.