No 100 mph is usually cited but it really depends on the speed rating of the tyre. The speed rating also reduces the load carrying capability in some cases.
You don't mention the year but assume '90s if it had 15's. 1996 specs say 3,065 to 3,393 for all coupes, so if it's a base, close to 3100 pounds. No way your passengers and cargo can weigh more than 1900 pounds unless you're hauling cinder blocks.
4000lb with 60/40 F/R weight distribution (wild guess, especially for fully loaded car) gives the front 2400 lb.
One front tire needs to support 1200 lb. Approximation.
5000 total 4 tire capacity = 1250 lb per tire
Now 1250 vs 1200 does not look like much safety buffer.
Krzyś
PS One would need real numbers to come up with needed load index.
4000lb with 60/40 F/R weight distribution (wild guess, especially for fully loaded car) gives the front 2400 lb.
One front tire needs to support 1200 lb. Approximation.
5000 total 4 tire capacity = 1250 lb per tire
Now 1250 vs 1200 does not look like much safety buffer.
Krzyś
PS One would need real numbers to come up with needed load index.