Quantum Break

I found a pretty good spot to farm this really quickly without any real danger of getting shot or having to avoid other enemies while trying to get this. Either load up the stage below on any difficulty or keep an eye out while you are playing the stage. Proceed through the level until you get to the part where you have to disable the Chronon Dampener and take out the enemies when you're looking for Dr. Amaral.

Once you jump down onto the platform right before the sphere (red dome) you will hit a check point making this the perfect spot to get it done really quickly. Basically all you do is walk into the dampeners field in front of you and wait for the enemy that is on the platform below you to turn around or walk up the stairs. Once he does this shoot the device (chronon harness) on his back, reload the checkpoint then rinse and repeat until your achievement pops.

Difficulty: Any
Required Amount: 15
Level: Monarch Gala - Act 3 Part 2

Whenever you find yourself in a stutter, and there are enemy guys roaming about freely, then they have harnesses you can destroy.

There are basically 3 kinds of enemies wearing harnesses:
1.) Normal enemies who simply move within stutters.
2.) Enemies with larger harnesses that can dash about, and be annoying.
3.) Juggernauts who you can only really take down by destroying their harnesses.

As I played through the game, I found group number 1 to be the easiest to farm. It only takes one bullet from your pistol to destroy their harness, and they are pretty dumb, even on Hard, so sneaking up behind thm is not that difficult.

Group #2 takes a few more bullets to take down, and you can not really stop them with your time powers. They are way to spastic to get consistent clean shots on their gear.

Group #3 are gimme's, but they are few and far between. I am almost done the game, on Hard, and I have only seen ~5 total. The big guys alone won't snag you this achievement. FYI: Using a shotgun or Light Machine Gun cuts them down fast. Using the Time Rush ability, I would simply run up behind them and fire away a couple of times, and they were toast

I found a decent place to grind this out was on the bridge during Act 4. Getting to this place has a few of the #1 enemies, but the sweet spot is after you make your way past the roadblock where the game saves, and you have 1 Juggernaut, 2 of the spastic guys, and 3-4 of the 1-hit wonders. There are also cars around that you can throw your time stop bubble around, fire off a few rounds, and get the Area Effect achieivement as well.

Questions, corrections and neg vote justifications below.

You can get this easily right after this enemy type is introduced. They're are five of them, so if you're accurate and quick you can restart from the checking just twice.

Three easiest way to expose their harness is to hit them with Time Shield, which throws them back. You can then Time Dodge into them, which has a good chance of turning them around, or you can dodge past them and turn around yourself. Their harness will be right in front of you and ready for shooting.

The best weapon is the shotgun, obviously, as a solid hit will blow up the harness in one shot.

Here's a video of me doing this: