engine dies in 15 minutes

[Shady Rascal]

You're either losing spark or you're losing fuel. Don't make it any more complex until you figure out which is the culprit.

When the thing dies, spray a spritz of carb spray or starter fluid down the carburetor. Does it try to start now ? If so, you have a fuel supply issue. If the spritz down the carb didnt cause it to try and start, pull a plug wire off and check for spark while cranking.