Get 15 kills in the same match WITHOUT dieing or you will need to start again. Don't get accidentally killed by your friends either (It happens trust me) just take turns getting 15 kills each then run and hide until the match is over, once it finishes the achievement will pop, This can be done in any game mode.
The hardest part is finding people who want to boost this crap game. Online matches require 8 people minimum, Must be in a ranked match.
If you find this solution to be unhelpful, please tell me why in a comment and I will update it the next time I'm online.