Not Kahuna, but from many years flying them, 52 X .015 are fine for a per plan "Peacemaker" powered by the plain bearing Enya .15 driving an 8 X 4 combo. .012 are lighter and arguably less draggy, but marginally thicker .015 lines (usually recommended as standard for class) won't ordinarily be a cause of the symptoms he is experiencing IME with either the "Peacemaker" in particular or that class of model generally.