This can be done in Forge with two controllers.Simply load up any map in Forge with two controllers, pick up a respawn point, press
and click 'Delete All Of These'. Find an open area to place a respawn point and place a man cannon pointing straight up underneath the respawn point. Get your second account to come stand on the man cannon and using your main account, shoot the second controller out of the air using a sniper rifle. They will respawn in the man cannon. Kill them 14 more times to get the achievement.