Cleaned Carburetor, Lawnmower Still Stalls

So I've had my lawnmower about 2 years. It's a push mower with a Briggs & Stratton 550EX engine.

My problem: the engine will run for about 15 minutes from cold. When it dies, it will crank for a couple of cycles and die again. Then I have to set it aside for the rest of the day because it's useless.

My actions: I've tried "Mechanic in a Bottle" and "Star Force" (comes in a blue bottle) solution to clean up the gas. I've tried removing all the gas and putting new gas in it. I've also removed the carburetor twice, pulled it apart, and sprayed it out with carb/choke cleaner. Cleaning the carb makes it run for a little while, but I keep running into the same issue.

I don't want to clean the carb every time I need to mow the grass. I also don't want to buy a new one or a rebuild kit if it's not going to fix my problem. Also don't want to buy a new mower if all I need to do is clean out something else.

I feel like my problem is simple but in a place I haven't looked. All signs point to carb. I've made sure that the passages through it are clear after I spray it out. I've taken off the spark plug and cleaned it.

So, I'm asking for help.