For anyone else interested in testing the page preview refresh times, here is a "borkified" version of the book that i've been working on:
https://1drv.ms/u/s!Ano7p-K16N1ojI9w...OZy2Q?e=5qtHdH
Please try the preview and see how fast is it on your machines. Try especially editing the Chapter 12 file, it gives me the worst preview loading time (3-4 sec.)