Game Manager

Hello,
i have a Project with diffrent scenes and i want to load this with a shortcut.
I wrote a Singleton StateManager which handle the active Scene and switching. When i switche the scenes four or five times it loads fast, but then every change load longer.
I need the same variable on different scenes, this is the reason for the StateManager.

Thanks for Help.

using UnityEngine;
using System.Collections;

public enum GameState
{
    Haus = 1,
    Auto = 2,
    Technik = 3
};

public delegate void OnStateChangeHandler();

public class StateManager : MonoBehaviour
{

    static StateManager _instance;
    public event OnStateChangeHandler OnStateChange;
    public bool isLeapControlling
    {
        get;
        private set;
    }

    public GameState gameState
    {
        get;
        private set;
    }

    public void SetGameState(GameState gameState)
    {
        this.gameState = gameState;
        if (OnStateChange != null)
        {
            OnStateChange();
        }
        Debug.Log("GameState geändert auf: " + gameState);
    }

    public void SetLeapState(bool leapState)
    {
        this.isLeapControlling = leapState;
        Debug.Log("LeapStatus: " + isLeapControlling.ToString());
    }

    protected StateManager()
    {
    }

    static public bool isActive
    {
        get
        {
            return _instance != null;
        }
    }

    static public StateManager Instance
    {
        get
        {
            if (_instance == null)
            {
                _instance = Object.FindObjectOfType(typeof(StateManager)) as StateManager;

                if (_instance == null)
                {
                    GameObject go = new GameObject("StateManager");
                    DontDestroyOnLoad(go);
                    _instance = go.AddComponent<StateManager>();
                }
            }
            return _instance;
        }
    }

    void OnApplicationQuit()
    {
        _instance = null;
    }

}

Is more easy if you copy and paste the code here for better reading, using insert… menu → code. Is an recommendation.