the 15 may be too big to fit. The FG-11 is about the same size as the OS 52 I have on it, but the ignition system its the problem, not much room for it and the tank up in the nose. Also over powering the LT-40 wont add much to its performance, with the 52 on it and a smaller prop I get some pretty good speed on it, but its a trainer, so don't expect much more than some nice tight loops, would need some major mods on the wing to get a better roll rate. One thing you would get is better vertical and maybe some good hovers. Mine hovers for a little bit before gravity wins.