Originally Posted by shenye
I think I know the reason for that. LRF are in binary format. In other words, with a new book, your reading device has to parse the "code" first and turn it into the intended text outcome. It may then cache the outcome to make subsequent loading and page turning faster.
LRFs are actually a single xml file in a binary wrapper, similar to epub (muitiple xml files in a binary wrapper). The slow initialisation is because a LRF is completely read and paginated when it is opened, so one screen equals one page. The same happens when you change the font size, which is therefore slow too.