Im trying to update enemy list but my code is realy laggy

I have enemy and npc spawners and in the list it updates to check if any new enemy have spawned to send the information to the ai.

 void Update()
      {
         GameObject[] enemyArray = GameObject.FindGameObjectsWithTag("Enemy");
         Enemies = new List<GameObject>(enemyArray);
         GameObject[] NPCArray = GameObject.FindGameObjectsWithTag("NPC");
         NPCs = new List<GameObject>(NPCArray);
         NPCs.Add(GameObject.FindGameObjectWithTag("Player"));
         //  Enemies = GameObject.FindGameObjectsWithTag("");
         setNpcListLength = NPCs.Count;
 
 
         if (Enemies.Count == 0)
         {
             Debug.Log("Player Has Won");
             SceneManager.LoadScene(SceneNumber);
         }
      }