Changing RawImage position killing frame rate on Android

Well the question is self explanatory, i m changing the RawImage.position in Update method and this is killing my frame rate and one of my level is not changing position as it doesn't have any RawImage in it and it is running smoothly, this means it RawImage.position which is dropping my frame rate ... basically i want background of my 2D game to move in random directions so i used RawImage and changing its position through script ... below is my script ...

     public RawImage cieRawImageTop, cieRawImageBottom;
 
     private Vector2 offsetTop, offsetBottom;
     private float speed;
     private Rect tempRectTop, tempRectBottom;
     private uint currNum, newNum;
 
     void Start(){
         speed = 0.0002f;
         setTopDirection ();
     }
 
     void Update () {
         tempRectTop.position = cieRawImageTop.uvRect.position + offsetTop;
         cieRawImageTop.uvRect = tempRectTop;
         tempRectBottom.position = cieRawImageBottom.uvRect.position + offsetBottom;
         cieRawImageBottom.uvRect = tempRectBottom;
     }
 
     void setTopDirection(){
         offsetTop = setDirection ();
         Invoke ("setBottomDirection", 1f);
     }
 
     void setBottomDirection(){
         offsetBottom = setDirection ();
         Invoke ("setTopDirection", 4f);
     }
 
     Vector2 setDirection(){
         Vector2 newOffset = new Vector2 (0f, 0f);
         newNum = (uint)Random.Range (0, 8);
         switch (newNum) {
         case 0:
             newOffset.x = 0f;
             newOffset.y = -speed;
             break;
         case 1:
             newOffset.x = speed;
             newOffset.y = -speed;
             break;
         case 2:
             newOffset.x = speed;
             newOffset.y = 0f;
             break;
         case 3:
             newOffset.x = newOffset.y = speed;
             break;
         case 4:
             newOffset.x = 0f;
             newOffset.y = speed;
             break;
         case 5:
             newOffset.x = -speed;
             newOffset.y = speed;
             break;
         case 6:
             newOffset.x = -speed;
             newOffset.y = 0f;
             break;
         case 7:
             newOffset.x = newOffset.y = -speed;
             break;
         }
         return newOffset;
     }