Game become slow after CapsuleCast on terrain?

I have a terrain object. when I CapsuleCast from camera to terrain the game slows down badly. However if I raycast other GameObjects it does not slows down? Does this have to do with terrain resolution or stuff?

     int i = 0;
             while (i < Input.touchCount) {
                 if (Input.GetTouch (i).phase == TouchPhase.Began) {
                         RaycastHit hit;
                         Ray ray = Camera.main.ScreenPointToRay (Input.GetTouch (i).position);
                         Vector3 p1 = ray.origin;
                         Vector3 p2 = ray.origin + (ray.direction * pickDistance);
                         if (Physics.CapsuleCast (p1, p2, pickRadius, ray.direction, out hit, pickDistance)) {
                                 Debug.Log ("hit something");
     
     
                                 }
                         }
                 }
                 ++i;