Tire wear/pressure

Run them at 60 psi. They will not run hotter at 60 than 80, since at 60 you will be well under the load rating for that tire at 60. When you have significantly more load rating than required there is zero reason to run at max pressure.

On a prior 21' trailer, I replaced 205 75R 15 C tires with 225 75R 15 E rated tires.
Ran 80psi with zero problems and the tires wore evenly. The extra ply rating and larger size gave me confidence that I had enough tire.

The only thing you need to be concerned with as far as your rims, is they should be at least 6" wide to accommodate the 225's.

Newer rims are stamped with a load rating, not a psi rating.

I run my trucks LT 'E''s at 65 but those are LT and not ST tires which might build up heat more than LT's. I think you reduce the weight rating by running the ST lower but not sure about the heat causing separation. Got to be careful on this one, jury might still be out.

A TT that light only needs a well matched OEM tire with a 10-20% reserve weight rating.
I run my OEM 'C' on a 50# rim at 45# in order to wear correctly.
Using too high (80#) tire is a bad idea on a 50# rim. Tire mfg of ST tires say you can use a 65# on a 50# rim but only if you need the extra rating due to a load or weight issue of a particular model TT.
Think about the hard ride an E offers to stress the lighter TT suspension components as well everything else inside your trailer. Like a tv ripping off a wall.
Its a TT, not a 5th wheel with H.D. suspension that can handle the use of an LT 80# e tire.

My ST tires are rated load range C at 50 psi and load range D at 65 psi.

I usually opt for the 65 psi which gives me a buffer on the tire pressure.

I agree with the previous statement, you will probably time out your tires before you wear them out.

He ordered 22575R15 Load range D, which upped the capacity by a rated 720 lbs. per tire. Maybe a bit of overkill, but should provide ample safety margin.

Not just a bit but a huge margin of over kill.
Tire experts tell us a 10-15 percent reserve capacity above the axle rating is plenty for tires on a trailer. I would agree.

The C gave the trailer 7280 lb capacity which is plenty of tire for a trailer that size.

The 225/75 D tire = 10160 lbs which is way too much tire.

Now the tire shop put a 225/75 E tire at 2830 lb capacity = 11320 lbs.

The E tires are a heavy tire and will run hotter at 50 or 65 psi than at max pressures.

Tell the guy to spend a couple of days and read this clickyhttp://www.rvtiresafety.com/search/label/Interply%20Shear. This blog eliminates lots of rv myth about tires (air pressures/load ranges/ply shear issues/etc) for our trailers.
Worlds of tech information about tires on trailers.

Max them out at 80 lbs. Under normal TT usage they will dry rot long before they wear out

Max them out at 80 lbs. Under normal TT usage they will dry rot long before they wear out

Well my first thought is a TT that came stock with load rated C tires will have rims/wheels that will more than likely only handle a few pounds more than the max psi of 50. Check psi stamp on inner or rear of wheel to determine it's max capacity.

Many do go up a load rating when they change out their ST tires to add to their safety margin, with many having the same query about psi. ST tires do deliver better heat handling and load bearing capabilities when aired to or near max psi.

Jumping up from C to load rated E tires is not so common and would be better if wheels designed to withstand the significantly higher pressure are installed along with the tires. ST tires are different than passenger/truck tires and longevity suffers with excess under-inflation.

We did go up a load rating on our TT tires and our rims were stamped with a psi that was just 5 pounds less than max psi on new tires. There are no ST tire police and they don't have to be filled to exactly max psi, but we do try to keep them close and thus far no blowouts or excessive wear.

An old rock crawler trick is to put a chalk line along the tread, then drive for a few hundred feet in a straight line. If the center is worn, pressure is too high. If the outside is worn, too low, and if the line is worn evenly, it's just right. I find most of my tires correct pressure runs in the 35-40 psi range.

First I'd make sure that the rims (wheels) that they mounted LRE's on are rated to even handle the 80 psi. That's a big jump from the LRC's that you originally had. (50 psi max).

However, you certainly won't need to air the E's to max for that trailer.