3d objects make games run slower?

Hi everyone!

My problem is, that i want to make a 2D android game, and if i use 3D Objects in it cause it looks far better in top down view, the game gets low on fps.

To describe it in detail:

I have a 10x10 map. Each element is a 3D game object. some of them is floor element (simple cube with texture) and some of them is wall (some wall model i created). And even if only 5-7 is enabled at once which is in the sight range the game gets down to 17-21 fps. Without them it runs easy on 60 fps. Does android hates 3D models? Or cellphones are too weak to render them? After 2 days of searches i don't even know what to think.

Hint: I tried to replace both the walls, and the floor elements, to default texture-less cubes (the default white cubes) and it also make the game slow to the same 17-21 fps.

I dont think that its relevant, but here is some code i use to create and store objects:

     public float CamSightRange;
     public GameObject Wall;
     public GameObject[] Floor;
     public GameObject Gate;
     public GameObject Camera;
     public GameObject Player;
 
     private GameObject[] Elements;
     private int[] map;
 
     private GameObject Walls;
     private GameObject Floors;
 
     // Use this for initialization
     void Start ()
     {
         Walls = new GameObject("Walls");
         Floors = new GameObject("Floors");
 
         Walls.transform.parent = transform;
         Floors.transform.parent = transform;
 
         GenerateArray();
 
         GenerateMap();
 
     }
 
 ...
  // i generate some 10x10 map as 1D [100] int array in the GenerateArray method
 ...
 
     private void GenerateMap()
     {
         Elements = new GameObject[102];
 
         for (int i = 0; i < 100; i++)
         {
 
             if (map[i] == 0)
             {
                 Elements[i] = GameObject.Instantiate(Wall, new Vector3(i % 10 * 10 + i * 0.002f, -i / 10 * 10, -0.6f + i * 0.001f), Quaternion.LookRotation(Vector3.back));
                 Elements[i].transform.parent = Walls.transform;
                 Elements[i].transform.Rotate (new Vector3(0,0,(Random.Range(0,4))*90));
             } else 
             if (map[i] == 1)
             {
                   Elements[i] = GameObject.Instantiate(Floor[Random.Range(0,Floor.Length)], transform);
                   Elements[i].transform.position = new Vector3(i % 10 * 10, -i / 10 * 10, 0);
                   Elements[i].transform.Rotate(new Vector3(0, 0, (Random.Range(0, 4)) * 90));
                   Elements[i].transform.parent = Floors.transform;
             }
             else
             if (map[i] == 2)
             {
                 Elements[i] = GameObject.Instantiate(Gate, transform);
                 Elements[i].transform.position = new Vector3(i % 10 * 10, -i / 10 * 10, -0.502f);
                 Elements[i].transform.parent = transform;
             }
         }
 
         Elements[100] = GameObject.Instantiate(Player, transform);
         Elements[100].transform.position = new Vector3(lastpos % 10 * 10, -lastpos / 10 * 10-3, -1);
         Elements[100].transform.parent = transform;
 
         Elements[101] = GameObject.Instantiate(Camera, transform);
         Elements[101].transform.position = new Vector3(lastpos % 10 * 10, -lastpos / 10 * 10 - 3, -3);
         Elements[101].transform.parent = transform;
         Elements[101].GetComponent<Camera>().target = Elements[100];
     }

the parent objects are some empty gameobject which help me to distribute different types of objects.