How can I make android app run with less than 20 fps

I've been trying to make my game run with a specific frame, when I try to run on unity, it works exactly like I wanted, but when I put in my Android phone, the frame goes to 25 fps or more...

I tried to use Application.targetFrameRate, and I've already change AndroidUnityPlayer.cs

I'm using this code using UnityEngine; using System.Collections;

public class FPSScript : MonoBehaviour {

 public float updateInterval = 0.5F;
 private float lastInterval;
 private int frames = 0;
 private float fps;

 void Start() {
     lastInterval = Time.realtimeSinceStartup;
     frames = 0;
     
     Application.targetFrameRate = 12;
     
 }

 void OnGUI() {
     GUILayout.Label("" + fps.ToString("f2"));
 }

 void Update() {
     ++frames;
     float timeNow = Time.realtimeSinceStartup;
     if (timeNow > lastInterval + updateInterval) {
         fps = frames / (timeNow - lastInterval);
         frames = 0;
         lastInterval = timeNow;
     }
 }

}