Here is the absolutely optimal way to boost this:
Create a ranked match
Game Type: Elimination
Players: any number of players works. Less players tends to be more efficient because you need to wait for everyone to find the lobby after every game, and in larger groups there tends to be someone every few games that takes some additional time.
Special Settings: set run speed to 1.5 and join grace period from 10 to 5 seconds.
When the match starts, simply jump off the ledge near the spawn. If you have a larger party, some people may spawn inside. These people are to throw a grenade at their feet. Games should take no longer than 6 seconds.
An additional tip: Jumping off the ledge should only take 3 seconds, but if you really want to shave time off, mash the jump button during the pre-match countdown. When the game starts, you should do a little double-jump right off the lendge, which should take 2 seconds. Not much of a difference, but hey, every second counts when embarking on such a grind.
The achievement should take around 10-15 hours of boosting.