AS2 - Rotate an mc with keystrokes

I’ve got a movie clip that I am rotating with the left and right arrow keys and it seems to be a bit buggy. Here’s the code:

var keyListener:Object = new Object();
keyListener.onKeyDown = function(){
    else if
    (Key.isDown (Key.LEFT)) {

In each frame it is rotated one degree and it rotates 15 degrees. But sometimes, instead of fifteen key strokes, it will rotate the whole range in 5 or even 3 keystrokes. Very frustrating! Is there a better solution for this?