So I'm looking into getting an electric trainer for my first plane - Hobbico SuperStar EP Select RTF w/Ailerons 50.

This plane uses 8.4v 2100-3600mah flat batteries (going to buy 1 or 2 extra so I have 2 or 3 total)

-Does more mah mean longer flight time?
-Can you interchange Nimh, Nicad, and Lipo? (which is better, Nimh or Nicad)?
-Is there any way to obtain 10-15min flight times with an electric trainer?
-Does it really take an hour to charge a battery when the advertisement says 15min?

Thanks.