Here is a video guide by Halo Completionist
who has done a guide for pretty much every achievement in the game.NOTE:
You probably have to complete the Prologue, Mombasa Streets, & Epilogue. For the Mombasa streets, I recommend completing it as fast as possible even if this part doesn't count. It's better to be safe then sorry.
Also keep in mind that this game is fairly short and if you're playing in coop and both know what you're doing, you may not even need to speedrun. I have been playing solo though and following these speedrun videos and have came 1st or 2nd on pretty much all of them against my friends who have the achievement.Tayari Plaza:Uplift Reserve:Kizingo Boulevard:ONI Alpha Site:NMPD HQ:Kikowani Station:Data Hive:Coastal Highway: