RE: Will this combo work?
The Kokam 700HC cell is rated for 6C or 4.2amps and the 1500HC cell is rated for 8C or 12amps. Remember that these are continuous current ratings and higher current delivery can be used for short bursts.
Besides the duration increase, you also have about a 2oz weight increase when using 3-cell packs. So, keep in mind the plane application as well when determining which cell to use.