You should easily get 12 miles on a 15ah pack @ 15-20mph. I had a 48v 1200w setup and constantly got over 30km / 19miles from it with a 12s / 15ah lipo drawing up to 2000w peaks.
A few things i learnt with the Cyclones (the 1200w atleast):
*Pedal - this really helps with range and speed.
*Use the gears - don't be lazy with gear selection and try not to lug/under rev the motor. Always start from a stand-still in 1st or 2nd gear.
*Don't bother using the 44t or 48t front chain wheel for pedaling, its too taller gearing for the motor to really pull.
Use the 44t or 48t to go to the 14t motor sprocket and use the 32t or 34t chainwheel to go to the back wheel.
I used a 32t and could still reach 64kph on a flat pathway with slick tyres on the bike. Its also much better for hill climbing.
*WOT for extended periods will see the motor starting to get quite hot, this could effect efficiency... The Cyclone heatsinks will help counter this, worthwhile getting.
I hope this helps