rallenty scroll main texture

Stupid question that I can not get out. I have a hanging object to 3 balloons and the background behind with a script mainTextureScroll to give the sense of upward movement. When a balloon is hit to slow the "ascent" of the object. how can I slow it down? I tried to decrease the variable scroll to slow down but there is the shot of the background to start from the starting point.

Code:
var balloonGreen : GameObject;

var balloonRed : GameObject;

var balloonYellow : GameObject;

 function Start(){
 
  
 
 balloonGreen = GameObject.FindGameObjectWithTag("Verde");
 
 balloonRed = GameObject.FindGameObjectWithTag("Rosso");
 
 balloonYellow = GameObject.FindGameObjectWithTag("Giallo");
 
  
 
  
 
  
 
  
 
 }
 
  
 
 function Update(){
 
  var test = Time.time * scroll;
 
  var testuno = Time.time * 0.10;
 
  
 
  
 
   
 
   
 
   renderer.material.mainTextureOffset = Vector3(0,test,0);
 
   
 
   
 
   if(balloonGreen.gameObject.renderer.enabled == false){
 
   
 
     
 
   
 
   
 
   
 
   }
 
  
 
  
 
 }