The way I went about getting this achievement was as follows:
1. Be sure to check dead bodies for Clutch Grenades by running over them
2. When you have one or more and come moderately close to some enemies stop time (LB + Y)
3. Walk right up to an enemy and throw the grenade at them (RB) This grenade will stick to them.
4. Back away so that you are not caught in the blast. When time starts again the grenade will explode and the enemy will die.
5. Repeat. Do this 15 times total and the achievement is yours.
Doing this I was able to get this achievement early on in the second act.
Alternatively it may be possible to just save at one point, such as in "New Blood" where you emerge from the tunnels to a group of enemies, where you have a Clutch Grenade, run out, stop time, stick the enemy, kill them, reload save, repeat. I have not tested this so confirmation would be great but I don't think it would reset your count if you didn't save, though it is possible.