Other than impact damage, brake track wear is what usually kills rims that have been laced properly. 15,000 miles is either a lot or not much depending on the terrain and weather you ride in. If you ride a lot of hills and in bad weather, the rims are probably pretty worn. If your area is flat, has low traffic and is clean and dry, they could last decades.

Inspect the brake tracks carefully and if they are smooth and flat the rims should be good. Also, inspect around the spoke nipples to be certain the rim shows no deformation or cracking there.

OTS is correct that butted spokes are easier on the rim and hubs than straight gauge.