Wow, 15min of run-time from a 2300mah battery is pretty good. Sounds like it's setup pretty well. If you can hold you finger on the motor for 2-3sec, you're certainly in the ballpark.
Two things to keep in mind: All temp guns are not created equal. Try to buy the best you can afford, preferably with a good recommendation. And check that your battery compartment can fit the 6500mah pack. The higher 2S lipos get from 5000mah it seems, the THICKER they get. You can buy 2S packs of 10,000mah, but it's as thick as a 3S. Have fun!!