The higher the last two digits of the model number, the higher the motors speed. Its easier to fly in confined space with a slower motor. Its more fun to fly a fast motor if you have a lot of space.
CL-0615-11 - indoors
CL-0615-14 - indoors/outdoors
150-205mAh mylipo batteries all work great on the Nano QX. The increased capacity of the larger cell is partly compensated of the additional weight, but there is still a net gain of flight time. A 205mAh battery will fly for 30-90 seconds longer than a 150mAh.
The 1-2g weight difference between the packs make a difference in flight behaviour. A heavier packs make for a faster, more stable flight outdoors, with easier and quicker descents. A lighter pack makes the quad more nimble and give an advantage during punch-outs.