Personally when this was first implemented i was against it being set to 15mins for all bosses. For some bosses like the quest bosses, aggy mordris and a few "hard" bosses i suggested raising the rage timer to 30 minutes. Or even lowering the timer as you level past the boss. So default timer would be 30mins, and say you were 50 levels above the boss it would be 15mins to kill the boss before he rages.
Rage is simply to stop underleveled players from attempting to kill a boss that is way out of their skill level. So a boost of 3-4 times dmg is fine. It basically wipes the group when they hit the timer, allowing a more experienced group to kill the boss.
OTM didnt look into my suggestion and neither did many testers but i believe the time does need some major fixes and would be best if it was changed based upon the player level in regards to the boss, which does factor in skill levels.
So, all I see is target lock is pointless on bosses.
No group of boss level players can kill that boss in 15 minutes. We took 40 odd minutes with 25 players 145-160 to kill the 150/160 boss.
I can't see a group of 8 level 160's would kill it within 15 minutes. The new system is really out of sync with what should be happening.
(disclaimer: admin stated in the past that a 6* boss takes ONE full balanced group not 2-3 groups)
Bosses need to be able to die with one group, 1 tank 2 Druids and 5 dps, no more.