RE: Mini Contender slimer conversion
A .10 might be a better match for that plane, but a .15 should do it if you are careful with the overall weight. The electric ARFs that I have convert so far ended up lighter than the electrical setup indication/recommendation. Most of them have had a rather high wing incidence though, setup to only hang from a larger prop rather than flying off the wing at higher speeds. So check the wing incidence first, it might be set-up as a rather slow flyer and then it will not respond well to more power, unless the wing incidence is altered.