1 Trailer hub running 15° hotter?

Without jacking it up and ck. endplay in bearings all you can do is pull hub cap off and drain what will run out into cutoff jug, then look at lube an replace lube with name brand hub oil and ck. temp again.

 

as long as you can hold your hand on the hub with out buring your hand you are OK, as off course there is oil in the hub

 

Nothing there to worry about, in my opinion. Could be one brake a little tighter, different type / weight oil in hub. If oil in hub, and not leaking, and no hotter than 120 degrees, I do not see a bad problem.

 

while its still warm stick a finger in the hole get some fluid on it, wipe it on a rag and hold rag in light to see if any shiny, if so pull and ck bearings-races be sure to clean and ck inner bearing race, look for discoloration, try to use syn dope back in there, its very important to seat [150-180] back off one round torque to spec for your setup-ie if two nuts inner nut to 55ft lbs, while there ck shoes return springs see if stretched any, look at drums outside for flacky light brown color and compare to other drums, if excessive replace shoes drum hardware for stretched springs allowing shoes to touch while rolling.

 

I'd also guess bearings.

 

Just for clarification, since there seems to be some confusion, is this a grease-packed hub? Not a more typical, modern set up with the plastic window, a red(usually) filler cap, that runs 75-90 oil? I think it's great that you are really on top of watching this, I recently was witness to a fire caused likely by a wheel bearing running dry. It's not a good thing to have happen. Unfortunately I don't know much about how to diagnose, or treat the old grease packed hubs, but if you verify that's what you have, I know there are lots here who can help you.