All You Can Eat
I found a video on youtube of someone doing the mission in 7 minutes and 43 seconds (about half the time required and faster than the fastest time on Halo: TMCC leaderboards, most likely still holds the world record)
There is a glitch in this video which I don't recommend trying, because I attempted it 2 times and fell to my death through the floor. Instead just run through the room, once you exit the room (without killing the enemies) go straight and left into the control room, kill everyone immediately and go to the front for the cutscene, and catch up to the video where he skips ahead.
While running through the mission grab a shotgun immediately (when the doors bust open which the hallway flooded with flood(no pun intended)). Use that while running through the mission to kill any enemies in your way. Don't forget to get the rocket launcher he picks up at 1:45 which will make the 4 objectives much easier.
Don't attempt the grenade jump, you will most likely die, if you notice he has 1 red bar left, he practiced this mission for a long time (he mentions in the video) to perfect everything.
Lastly If you want to at the end of the mission, you can try the Warthog squeeze (at the last stretch) but I was unable to do it and ran on foot.
Going through the entire mission the first time using this video it took me 16:50. The second time learning from a couple of mistakes I did in 11:21 (#142 on the world leaderboards for fastest time on Halo: TMCC)
Following the video and my tips should help you get easily under 15 minutes, if anyone has a problem doing it just say which part you messed up on so I can add it and others won't make the same mistake.
Also if you do the end exactly like him you will also obtain this achievement: