LEGENDXKILLA II 360's Guide
Easy way to get this without having to go back to the start of the chapter.
This is obtained on the second to last level "Housewares"
Follow your objectives until you enter a Bistro. Go downstairs, enter 3958 into the keypad so it opens the door to the room that contains the Radar Range, but do not enter..
Now close the vent to your right, which will be your objective, this now saves your profile.
Go back to the room with the keypad and pick up the Radar Range. This will trigger 3 enemies in the room behind you. Simply hold RT until one of the enemies turn red, it will then explode causing a chain reaction, you should get 2/15 toward this achievement right there and then.
Now simply restart checkpoint and re-enter the room with the keypad which should be open, pick up the Radar Range again, rinse and repeat. Should take no more than 5 minutes to get what you need.
As a side note. I didn't have any upgrades on this weapon and I had 10/15 after a playthrough on normal.
With a little luck, you could possibly get 15 by the end of the game, but this solution is there for the people looking to get this achievement with the minimum of fuss.