When you first use Foliobook, the speed of the image transitions is set to quite a slow setting. You can easily speed this up to a setting that feels right for you. 

When you are in the image gallery (slideshow),  double tap to show the toolbar, then select the style menu (pencil icon)

Select 'Slideshow' and you will be able to speed up the amount of time the image is displayed, and also the amount of time the transition takes from one image to another

You can also change the type of transition. Some types look better fast, and some look better slow, its best to experiment to find what suits your material the best.