In my opinion, don't fly lipo and you have less to worry about: no overburning your motors, not overheating your electronics, no power cutoff in flight. If you have more money than that to pour in, that's another story.

BTW, can you fly 15 min in one go? Or do you really want to burn you heli that long?

15 min or more flight time is easily achieved with two Nimh packs. Take a break, it's good for the wellbeing of your heli and your own health.