Create a ranked CTF game on the "rubble" map. Set run speed to 1.5, flag captures to 16, time limit to 20 minutes.
This is quickest when boosting in a group of 2 players.
Each player capture 15 flags. One player capture a 16th to end the game.
Repeat the process 4 times and it will pop for both. You can even use some extra time on the 4th round to get some turret kills if you want :)