I change formats of single letters or total paragraphs in a book. If I do this at a start of a indesign file (70 pages, 270 footnotes, no pictures, only opened part of the book) it lasts up to 40 seconds until I can work further. If I do this further to the end of the document the delay is lessens.
My Win-10-PC has 16 GB RAM and i7-processor