On a trailer, I don't think you or the trailer will notice one tire being slightly larger. If the tires are getting older, perhaps for peace of mind I would change the other tires as well, but that is up to you. I don't let mine go past 5 years from the date on the tire. It is unlikely the extra 15 psi will be an issue for the rim. It is pretty rare to hear of a rim failure. I couldn't find a load or pressure rating on my rims and I went from LRC to LRD (50 psi to 65 psi) and I've had no issues. Good luck with whatever you decide.
