Use Calibre to compress images within the EPUB.
It is tempting to type "free" before that keyword. But here is the hard truth: T L Swan is not a faceless corporation. She is a self-published or indie-published sensation (depending on the territory) who relies directly on sales and KU (Kindle Unlimited) page reads to write the next book. my temptation by t l swan epub portable
Use Calibre to convert the EPUB to EPUB again. This "polishes" the file and fixes code errors. Use Calibre to compress images within the EPUB