I've had several pro 15's and HSN should be between 2 and 3, LSN should be about 2. Whenever I had a problem tuning mine I pulled the carb and cleaned it completely by pulling both LSN and HSN and spraying carb cleaner into all openings on carb to flush out crap. Replaced all o rings (traxxas sells a complete set of replacement o rings). My pro 15's were usually at 2.5 turns for HSN and about 2 or a bit less (1 7/8) for LSN. Idle opening was about 1/16 inch wide.

You might have compression issues. Do you know how many gallons of fuel it has seen. It sounds like it's getting hot and stalling out. That could be a worn engine or you're overheating it.