Unfortunately, sometimes it's a bit much. Even playing T3 or T4 with my average gear, I can certainly have elites that die before the 15 seconds are up. Then I am looking around for things to kill while it's active before I even stop to loot, so I don't feel like it's wasted.
Anyone else feel it would be better if it were not so extreme?
I propose a 60 second cooldown and a 12 second duration, instead of a 90 second cooldown and a 15 second duration.
I rather have it run out when the enemy is almost dead and have it on a shorter CD, than have it spill over excessively and find myself stuck with a boring CD. At worse the change slightly weakens it against rift bosses, but it would still be better off.