I see it this way:
If the content is hard you'll be moving slow enough that it will recharge.
If the content is easy you'll be moving fast enough that you can keep refreshing it.
On bosses it will likely always be up unless there's some stupid mechanic where you don't hit something for 15 seconds, and even then the cooldown starts from when you cast it, not from when it drops off, so it will probably be back soon. (and if you're not hitting stuff it's not like you're using much mana, and you probably aren't taking that much either).
I'm happy. As long as it stacks with sanctuary, and if it doesn't, just means I always have kings.
_________________
No really, I'm not
addicted.