Size doesn't mean quality (yeah, narrowly avoided that pun). But really, if there is 10gb extra that would heavily tax any connection and storage, for nothing, if its a bug, the dev should be ask help.
If the fix sup3erbreakout mentioned does work, the dev should implement it as fast as possible, if not then seek help elsewhere.
With the amount of content this could easily be cut down to a 1.5 gb renpy game, without loosing quality, content or options.
Some unity games seem pointless when there are better engines for the content.