Scroll lags

When scrolling through the pages it lags. Basically it takes 5-10 scroll on the mouse to get down one page when the view is set to 'fit to width'. When it's fit to one page one scroll on the mouse makes one page jump - but it lags while doing it.

The sample book (how to get started) works fine however.

How to solve this problem. I'm using a MacBook pro that has all the necessary requirements.