The low speed needle in recessed in a hole on the side of the carb opposite where the fuel line hooks up. You'll need a small screw driver to reach in there. 15 seconds to quit sounds like you are too righ at idle. You need to get a small, flat, screw driver and turn this screw in, clockwise a quarter turn.

Open the top end up a quarter turn. Any time you quit up in the air at full power, it is usually either running too lean or a fuel line/tank problem.