So I've spot-checked another couple dozen images, and I think I've got a decent handle on the compression artifacts as a result. There is certainly a "noticable" reduction in quality, but personally I wouldn't characterize it as drastic If that level of quality reduction is outside of what you can artistically accept, I and most of your other fans would fully understand and accept your artistic control.
From what I saw, there's a definite reduction in image quality with respect to lighting and textures within your renders. Some shapes seem to be oddly smoothed at this level of compression as well, and take on a more cartoonish and less photo-realstic feel as a result.
On the other hand, as the project develops you might revisit the compression issue with the workflow, logistical, and business aspects of releasing a 7.5GB .zip file in mind. For instance, I've noticed you've recently discontinued .apk Android releases of Harem Hotel because the file size has gotten too large. I play on PC, so it doesn't affect me. However, it might be possible to return to releasing .apk distributions of the game (assuming you find the effort worthwhile) by using this level of compression to significantly reduce that file size. I imagine some Android users would prefer a reduction in image quality over dropping .apk releases (of course you know better than I do). The small screen sizes of Android devices might also make the compression artifacts less significant.
If you're running into similar file size limitations or find yourself adjusting your workflow significantly to work around the challenges of managing such large builds it might be worth re-evaluating your compression level. If not, well, I've got fiber internet anyway, and I'm willing to wait an hour or two to experience new releases of your great game. I just thought I'd bring it up in case you're starting to feel large build sizes weigh down your creative process.