(just erased a long response--ARGH!!!!)

I think you have too much pressure on your pump 25-30# is, IMHO, too high. For a 15,000 gal pool and 1 hp pump that tells me something simply is just plain wrong somewhere. I have 19,000 gal, a 1hp SuperPump (Hayward) 2 speed and a 200# sand filter and I'm going into 6 years with no problems. When I hit 25# I backwash immediately!

Something is causing your excessive pressure and I think that's burning out your motors. It may be a blocked pipe, improperly routed plumbing, or too small a filter or a blocked filter, but probably not a bad pump. Can you disconnect key parts of the system and see if the pressure changes? If pressure jumps excessively, you've probably found the problem and blockage.

BTW, what filter are you running (type, brand, size and model)and is your pump a 1hp full-rated or up-rated?

Al, what do you think?