Destroying objects, clearing an array

Hello,

I'm working on a very simple game. It displays 15 buttons and one of them is covered with a different sprite. It works fine for one round. But on the next round, i want to clear the array containing the 15 buttons to set a new one. And it s not working, i'm getting 15 new buttons on each round ( so it makes 30 buttons on the second round, 45 on the third...). I guess that my destroy function doesn't look for the good gameobject ( it's located in the "reussi" method) Thanks for your help !

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using UnityEngine.EventSystems;
 
 
 public class InitBouttons : MonoBehaviour {
 
 public Button prefabBoutton;
 public Button[] listeBouttons;
 public Transform monpere;
 public Sprite recouvrement;
 public GameObject pannelReussi;
 public GameObject pannelTemps;
 Text montexte;
 
 int tirageAuSort;
 int score = 0;
 
 float timeMax= 15f;
 float timeRemaining ;
 
 bool reussite= false;
 
 
 
 
 void Start ()
 {
 
     montexte= pannelTemps.GetComponent<Text>();
     timeRemaining=timeMax;
     initialisation();    
 }
     
 
     void Update ()
 {
 
 
         if (!reussite) {
             timeRemaining -= Time.deltaTime; // on soustrait au temps restant en secondes
             UpdateTimeRemainingDisplay ();
 }
 
 
 
         if (timeRemaining <= 0f)
 {
             Debug.Log ("gameover");
 }
 
         if ( reussite && Input.GetMouseButton (0) )
         initialisation();
 
         
 
 
                 //if (EventSystem.current.currentSelectedGameObject.name != null)
                 //Debug.Log (EventSystem.current.currentSelectedGameObject.name);
 
                 //if ( EventSystem.current.currentSelectedGameObject.name == listeBouttons[tirageAuSort].name) Debug.Log ("bravo!");
 
 
         
             
         
     }
 
 
     void initialisation ()
     {
         pannelReussi.SetActive (false);
         reussite = false;
         listeBouttons = new Button[15]; 
 
 
         for (int i = 0; i < 15; i++) 
 
         {
             listeBouttons[i] = Instantiate (prefabBoutton);
             listeBouttons [i].transform.SetParent (monpere, false);
             listeBouttons [i].name = "" + i;
             Debug.Log (listeBouttons [i].name = "" + i);
 
 
         }
 
 
         tirageAuSort = Random.Range (0, 15);
         //listeBouttons[tirageAuSort].GetComponent<Image>().color = Color.black;  si on veut changer la couleur
         listeBouttons [tirageAuSort].GetComponent<Image> ().sprite = recouvrement;  // on change l'image
         listeBouttons [tirageAuSort].onClick.AddListener (() => Reussi ());
         
     }
 
     bool  Reussi ()
     {
         pannelReussi.SetActive(true);
         score ++;
           reussite = true;
           timeMax --;
          timeRemaining = timeMax;
 
         for (int i = 0; i < 15; i++)  // the loop to destroy clear the array by destroying the button
              {
                 Debug.Log (" J'efface le bouton " + listeBouttons[i].name);
                 DestroyImmediate (listeBouttons [i]);   
 
             
              }
 
         
 
         return reussite;
 
 
         
 
 
 
     }
 
  void UpdateTimeRemainingDisplay()
     {
       montexte.text = "Temps restant: " + Mathf.Round (timeRemaining).ToString (); // on affiche le tempts restant, Mathf.round arrondit
     }
 
 
 
 
 
 }