Random.Range when instantiating things at start freezes the game

Hey i got an problem with instantiating prefabs (trees, rocks, bushes) on startup. I have a script to do it:

using UnityEngine; using System.Collections;

 public class raySpawn : MonoBehaviour {
 public GameObject[] propy = new GameObject[30]; //Array of prefabs
 private Vector3 origin;
 private int index = 0;
 private bool czyIndexPoprawny = false; //currently unused
     // Use this for initialization
     void Start () {
         origin = gameObject.transform.position;
         RaycastHit hit;
         for(int i = 0; i < 4000; i++)
         {
             Ray linia = new Ray(gameObject.transform.position, new Vector3(Random.Range(-1000,1000), -500, Random.Range(-1000,1000)));
             if(Physics.Raycast(linia,out hit) && hit.transform.tag == "ZaczepBudowy") //If it hits terrain
             {
                 if(hit.point.y > 24) //So things wont generate at sea level
                 {
                     index = Random.Range(0,12);
                     //if(index != null)
                         Instantiate(propy[index],hit.point,Quaternion.identity);
                 }
             }
             else
                 i--;
             
             //Debug.Log(Random.Range(0,11).ToString()); I checked if its something horribly wrong with Random.Range itself
         }
     }
 }
 

Theres currently 12 objects in array (0 to 11). I dont know why, but Random.Range(X,Y) includes the X but excludes the Y, so i have to add one digit to it. When i put 10 as a Y, it works (only 9 of 12 will spawn) but when i put 11 as Y, the game freezes horribly and makes F and S in FPS switch place. (Seconds per Frame ¯_(ツ)_/¯ ). I seek an solution for this. I checked if one prefab of those is causing a massive lag, but i found that not one of the prefabs is causing the problem. Unaccounted takes up to 95% of memory in the profiler. I dont know why