AI Target Finding Optimization

I currently have AI that determines who is closest between the two players in COOP, but having 6+ enemies on screen brings the game to an absolute crawl suddenly.

I've tried multiple ways to optimize and slow this process down, and it is running through an Invoke Repeating.

 function findTarget () { 
     // Distance and Quaternion Rotation math
     var distance = Mathf.Infinity;
     var position = transform.position;
 
     // Transforms the enemy toward the ground should they be lifted.
     if (!isGrounded) {
         transform.position += Vector3.down * 8 * Time.deltaTime;
     }
 
     // Finding nearest player
         for (var _player : GameObject in _players) {
             var difference = _player.transform.position - position;
             var currentDistance = difference.sqrMagnitude;
 
             if (currentDistance < distance) {
                 nearestPlayer = _player;
                 distance = currentDistance;
                   target = nearestPlayer.transform;
 
                   Debug.Log ("Nearest " + nearestPlayer);
                   Debug.Log ("Target is " + target);
 
                 // The enemy now has a target 
                 var distance2 = Vector3.Distance(aiTransform.position, target.position);
                 var dy : float = target.position.y - aiTransform.position.y;
                 var dx : float = target.position.x - aiTransform.position.x;
                 var angle : float = Mathf.Atan2(dy, dx);
 
                 if (distance2<=range && distance2>stop) {
 
                     // The enemy is rotating constantly toward target
                     transform.rotation = Quaternion.Slerp(transform.rotation,  Quaternion.LookRotation (target.position - transform.position), rotationSpeed * Time.deltaTime);
                 
                     var time = moveSpeed * Time.deltaTime;
 
                     transform.position = Vector3.MoveTowards(transform.position, target.transform.position, moveSpeed * Time.deltaTime);
 
                     enemyAnim.SetBool ("chasing", true);
                 
                 }    
             }
 
         }    
 }