I think it is 5 minutes, 15m is the time it takes in WoW to be able to kick.
I just had a lengthy discussion about this topic in the official forums and I still maintain that it is more efficient to drag the underperformer through compared to waiting for a refill (esp if it is a tank) and risking an aborted run.
Don't get me wrong:lazy play aggravates me as much as the next @
Wrecktangle but ultimately, it's a friggin dungeon, we won't wipe and I'll have some other entertainment running next to the window anyway. So big whoop.
I do get a chuckle now and then watching ACT trying to figure out how any person can be THAT bad.