Build very slow at startup

Hi,

Unity 2019.3.15f1

I'm making a 3d sport game where my main scene contains my UI and my empty arena (floor + goals, low poly models).

I also instantiate a lot of objects at startup to create a pool a 3d objects to be used later so there is almost no loading time since i'm going to reuse all the objects all the time:

Code (CSharp):

1. void Start () {
2.         StartCoroutine(this.initPools());
3.     }
4. private IEnumerator initPools()
5.     { // let's wait for a few frames
6.  
7.         yield return null;
8.         yield return new WaitForSeconds(0.2f);
9.  
10.         this.poolDictionary = new Dictionary<string, ObjectPoolItem>();
11.  
12.  
13.         int nbPooled = 0;
14.         foreach (var pool in pools)
15.         {
16.  
17.             Queue<GameObject> queue = new Queue<GameObject>();
18.             for (int i = 0; i < pool.amountToPool; i++)
19.             {
20.                 GameObject obj = (GameObject)Instantiate(pool.objectToPool);
21.                 obj.transform.SetParent(this.transform);
22.                 obj.tag = tagPooledObject+ pool.typeObject.ToString();
23.                 obj.SetActive(false);
24.                 queue.Enqueue(obj);
25.             }
26.             pool.ListPooledObjects = queue;
27.             this.poolDictionary.Add(pool.typeObject.ToString(), pool);
28.  
29.             nbPooled += pool.amountToPool;
30.             if (nbPooled > 1000)
31.             {
32.                 nbPooled = 0;
33.                 yield return null;
34.             }
35.         }
36.  
37.     }

It works very well in the editor but I experience a "slow" start with the built game (windows/mac) (I guess some objects are already loaded in the editor which explains why playing is fast) so I was wondering if I was doing anything wrong with my approach or which tools I could use to figure out what actually takes time when loading the game (black screen that could freeze the game for like 5-10 s).

My pooled objects could be small 3D assets, more detailed 3D objects (just a few of those) or UI components (buttons to be used in tables for instance) so there could be quite a lot of components. Delaying the load doesn't really seem to make the game start much faster but maybe I haven't delayed enough or I should put more yield in between instantiations. I thought that putting my coroutine in the Start and wait for a few frames would help but it doesn't seem to really improve the start.

I guess it would just be easier if there is a tool somewhere that I could use to see in detail what is slow with the built version of the game.

Thank you for your help!