The file shown here is an epub at 777 kb. The actual download is 85 mb, probably because it has 23 embedded fonts. (Four of them seem to be Noto's Japanese fonts, which are over 15 mb each. One more is a 10 mb unnamed font that's corrupt when extracted; looks like another Noto variant.)
Removing those knocks it down to a more reasonable 4.5 mb (there's still a lot of embedded fonts, but most of the rest are probably in active use, and I'm not taking the time to sort out the details) and doesn't seem to cause any problems.
Let me know if you'd like a copy of that one.