This style actually used to use much less stamina, to the point where you could switch between the proc and flurry endlessly. Flurry lasted for a few fights, and after that you could regen it stamina via switching to proc. In essence, you could keep up a style permanently.
Now as for your concerns, at level 65 with about 200 stamina I can keep it up endlessly, or there abouts anyway. Probably lose about 1 stamina per fight. Actually you know what, I don't even really know because our 15'th style is located next to FD so while pulling I tend to hit it a few times. This of course drains my stamina and then yeah.. anyway, it lasts a long time.
Also, if you're not tanking I suggest using your offensive style over the proc, or at least use the offensive one to gain your stamina back, then switch to the proc.