First off. Going plus will raise the trailer. Mileage may change. But RV people wouldn't be RV people if we cared too much about the overhead
I also thought about doing this once and decided not to - just because it would be aerodynamically higher (higher profile), and harder to reach the first step. The first step was already tricky for the kids and didn't want to challenge them more. Also, you might need an adjustment at your shank to level the tow after the switch. But that would be easy to fix.
As for the benefit: well you get .5" more clearance. Hmmm. I like the "look" though. Especially with nice aluminum rims, chrome lugs, trim ring. yup. You wll increase your safety margin and never come close to overloading the wheels (but limit is unchanged for axles, spindle, brakes, studs, etc)- tire life may increase and tire temps will not be any problem you'll see. Unless you're speeding.
As for the tire discussion: You stated you were shopping for D or E rated 15" tires - trailer tires already have appropriate sidewall configuration for trailer use. Max load on wheels smaller than 16 (16.5??) CANT use higher rated tires because the wheel would fail. So why manufacture a tire that is rated higher than a wheel could carry anyway. Anthing heavier would be on larger assemblies, right? The wheel itself couldn't take it. I know you don't mean to overload your current 15's, I was just discussing why one cant find E tires for 14" rims. None being manufactured. I am surprised you found ANY E rated tires for 15" wheels. There are 16" (16.5"?) wheels - and tires to go with them. I would confine my shopping decisions to those, personally.
"But, I am not a real doctor. I have a degree in science."
Please reply later any share what you worked out.