RE: GS15R engine or GXR15 engine??
Ok.
I have experience with kyosho engines. They are reliable runners, but don't last long, and are pretty weak.
My advice? Get the KIT version, and run the engine till it dies, then swap it for something like an O.S. .12 CV-R or a .15CV-R
I did something similar, O.S. engines are just so much better in every way.