Simple movement causing lag (on standalone)

I have 100 AI simply moving towards player.
First i used character controllers to move the AI (with SimpleMove). FPS dropped to 28.
Then i removed the SimpleMove from the script and had only look rotation. FPS stayed at 60.
So, problem seems to be at moving the AI.

I tried with rigidbody + capsule collider and moved the AI with transform.Translate. Again FPS dropped to 28.

So what could cause this?

EDIT: I tried with only transform.Translate. On editor i had +60 fps.
When i build the game, it is like a slideshow…

I believe just line 6 slowing you down. calling Quaternion.LookRotation every frame is too much.
try refreshing the rotation variable every ten frames or so. and you pry wont notice a difference with slerp.

put line 6 in a timer like this:

if (timer==0){rotation = Quaternion.LookRotation(dir);}

if(timer==0){timer = 10;}