Loading levels asynchronously in android VR game

Hi i have a project with four levels namely Scene_A, Scene_B… I have setup a javascript timer to shift from each scene to the next,

#pragma strict
var timer : float = 5.0;
function Update () {
timer -= Time.deltaTime;
if(timer <= 0 ){
Application.LoadLevel("Scene_B");
}
}

This is the script i have used to change from scene to scene. The timer is kept based on the time that i have given the player to see the content. Some levels are big and take up a huge time loading that too on an android . Is there a way to asynchronously load level B while level A is still playing(may be a few seconds till Level B loads) so that i can have a kind of smooth transition . Kindly help me out in this thing. I tried async operation but it seems like it works in pc but not on my android device Because in pc the load time is verysmall so not noticeable

hi yes right now i am using the scenemanager script , with c sharp , instead of javascript. and tried using the loadsceneasync command . it was loading the scene continously not allowing me to play it . like stuck at the beginning it kept on loading till i exited.
using UnityEngine;
using System.Collections;
using UnityEngine.SceneManagement;
public class city : MonoBehaviour {
public string SceneToLoad = “Scene_D”;
public float DelayTime = 25.0f;
public void Start() {
StartCoroutine (“Wait”);
}
private IEnumerator Wait () {
yield return new WaitForSeconds(DelayTime);
SceneManager.LoadScene (SceneToLoad, LoadSceneMode.Single);
}
}
that the one i use now. and when i use
SceneManager.LoadSceneAsync (SceneToLoad, LoadSceneMode.Single); it kept on loading , i dont know what i am missing . is there a seperate function or operation i need to call for to use thisLoadsceneAsync command.