Is there a message/event that I can wait for when object is created in the scene ?

I have written A* pathfinding algorithm. I have my obstacles defined as GameObjects with Tag Obstacle. I would like to update the obstacle map every seconds or so IF an obstacle has been moved or created/deleted.

I am now doing something like that :

 if (stopwatch.Elapsed.TotalMilliseconds - lastMapUpdateInMs > PathFinderConstants.timeForObstaclesUpdateInMs) {
     int i = 0;
     foreach (GameObject go in obstacles_) {
         if (    go.transform.position != obstaclesCachedPos_ [i] ||
                 go.transform.rotation != obstaclesCachedRot_ [i]) {
             regenerateMap = true;
             obstaclesCachedPos_ [i] = go.transform.position;
             obstaclesCachedRot_ [i] = go.transform.rotation;
             break;
         }
         i++;
     }
         
 //             this only works for dynamic adding of obstacles, to be able to remove them change that
     GameObject[] goarr = GameObject.FindGameObjectsWithTag (PathFinderConstants.obstacleTag);
     if (goarr.Length != obstacles_.Count) {
         regenerateMap = true;    
         obstacles_.Add (goarr [goarr.Length - 1]);
         obstaclesCachedPos_.Add (goarr [goarr.Length - 1].transform.position);
         obstaclesCachedRot_.Add (goarr [goarr.Length - 1].transform.rotation);
     }
         
     lastMapUpdateInMs = stopwatch.Elapsed.TotalMilliseconds;
 }

But this slows down the application considerably. How con I do this in other way ?