SceneManager.LoadSceneAsync()の読み込み速度の向上を行いたい

private void sceneManagerLoad()
{
    sceneManagerLoadAsync();
    sceneManagerLoadAsyncFast();
}

private void sceneManagerLoadAsync()
{
    loadSceneAsyncFlag = false;
    StartCoroutine( loadSceneAsync( "logo" ) );
}

private void sceneManagerLoadAsyncFast()
{
    _loadSceneFastAllowSceneActivation = false;
    StartCoroutine( loadSceneAsyncFast( "main" ) );
}

public IEnumerator loadSceneAsync( string a_scene )
{
    yield return null;
    AsyncOperation asyncOperation = SceneManager.LoadSceneAsync( a_scene, LoadSceneMode.Additive );
    asyncOperation.allowSceneActivation = true;

    bool l_isDone = true;
    while( l_isDone )
    {
        if (asyncOperation.progress >= 0.9f)
        {
            l_isDone = false;
        }
        yield return null;
    }
    yield return null;

    while (!asyncOperation.isDone){
        yield return null;
    }

    yield return null;

    unloadScene();
    yield return null;

    loadSceneAsyncFlag = true;
}

public IEnumerator loadSceneAsyncFast( string a_scene )
{
    yield return null;

    AsyncOperation asyncOperation = SceneManager.LoadSceneAsync( a_scene, LoadSceneMode.Additive );

    asyncOperation.allowSceneActivation = true;

    bool l_isDone = true;
    while( l_isDone )
    {
        if (asyncOperation.progress >= 0.9f)
        {
            l_isDone = false;
        }
        yield return null;
    }

    while (!asyncOperation.isDone){
        yield return null;
    }

    while (!_loadSceneFastAllowSceneActivation){
        yield return null;
    }

    _loadSceneFastFlag = true;
    unloadScene();

    loadSceneAsyncFlag = true;
}