Poor frame rate

Hi guys,
I have an “onEnterFrame()” function in one of my movieclips which calculates my mouse position and sets off some script according to the position.

Unfortunately this code is slowing my movies frame rate from 30 to about 15 and I am unsure of how I can recode this so it won’t slow down the movie.

Basically I have a rectangular movie clip that slides from left to right depending on the users _xmouse. But I only want it to execute while the mouse is over that particular movie clip.

Here is my code below. The rectangular movie sits at the bottom of my stage so all I am doing is working out if the _ymouse is below the _y of the movie…if so the code executes.

I am sure there is a better way to do this. But not sure how.

this.onEnterFrame = function(){
mse = _xmouse; // get _xmouse

if(_parent._ymouse > _parent.eventSlide._y){

//if _ymouse is below movie clip
events._x = evntwdt;
events._x = events._x + 5;
events._x = 0;
events._x = events._x - 5;