My 4 year old lawnmower gets hot and dies. I can mow for 15 minutes
and it coughs and sputters and then shuts down completely and will not
restart - for 15 minutes. Then it will start and runs another 10
minutes.

Seems to be a heat related issue. I cleaned out the debris and
replaced the spark plug. No change.

What could be wrong and how do I determine it?

Sherman