touch control code optimization

hi, i have a super simple scene 7 boxes , 1 sphere and all have mobile / unlit shader , no light in scene.

here is my script for controlling a sphere.

 using UnityEngine;
 using System.Collections;
 
 public class PlayerControllerTouch : MonoBehaviour {
 
     public float speed;
 
     void Update() {
 
         if (Input.touchCount > 0){
             transform.localScale += new Vector3 (0.0f, 0.0f, 0.0f);
         }else {
             transform.localScale += new Vector3 (0.0035f, 0.0f, 0.0035f);
         }
         if (Input.touchCount > 0 && Input.GetTouch(0).phase == TouchPhase.Moved) {
             Vector2 touchDeltaPosition = Input.GetTouch(0).deltaPosition;
             transform.Translate(touchDeltaPosition.x * speed,0,touchDeltaPosition.y * speed);
         }    
     }
 }

from a ortograhpic camera from top i'm controlling a sphere with my touch , this simple scene is not smooth on htc m7 , galaxsy note3 even note 4, i have htc m8 and game flows very smooth.

all i'm doing with script if i stop touching screen i start scaling the sphere and move sphere with touch.

any idea that cause lag? thank you.