Unity OnMouseDrag too fast for Update function

I have two sprites and I am rotating them on mouse drag. When I rotate one, another has to rotate also but a bit slower. The issue is when I move first sprite too fast. I guess Unity skips some points where I ask for current rotation of object. Here is the code:

 if(objekatKliknut=="Minute"){
         mouseClickPos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
         Vector3 dir = mouseClickPos - transform.position;
         angle = Mathf.Atan2(dir.y,dir.x) * Mathf.Rad2Deg;
         angle-=90;
         if (angle < 0.0f) angle += 360.0f;
         angle = Mathf.Round(angle/6.0f)*6.0f;
         if(angle==360) angle=0;
         hand1.transform.rotation = Quaternion.AngleAxis(angle, Vector3.forward);
         a1=angle;
         if(a1!=a2){
             float x = Mathf.Abs(a1-a2);
             if(a1>a2){
             moveRight = false;
                 if(x==6){
                     handRot+=addAngle*x/6f;
                     globeRot-=addGlobeAngle;
                 }
                 a2=a1;
             }
             else if(a1<a2){
             moveRight = true;
                 if(x==6){
                     handRot-=addAngle*(x/6f);
                     globeRot+=addGlobeAngle*(x/6f);                     
                 }
                 a2=a1;
             }
         }
         hand.transform.rotation = Quaternion.AngleAxis(handRot, Vector3.forward);
         oblaci.transform.rotation = Quaternion.AngleAxis(globeRot, Vector3.forward);
     }

hand1 is first object that I am rotating, and hand is the second one that needs to be rotated relative to the first one. Problem is in that x==6 because I rotate object for 6 degrees, and when I move the mouse fast enough Update() can't read it fast enough and object rotates for more then 6 degrees.