I'd guess the "meat" of the 7.5GB is probably basic stuff like engine and main assets, so if the next chapters release as updates or something similar that keeps everything to the same .exe, then I think it'll be lower, but if each chapter is its own standalone file I think it'll remain about the same all throughout, maybe even increase in filesize depending on how big the chapter is.
but I know barely anything about game development to be sure of what I'm talking about here lol, just guessing stuff