I just forked a big project for simplify it but the result is still more than 1Go on my organization account.
I suspect than compressed textures are still in memory inside the project despite the fact than I removed 90% of them.
When I download the build or archive the project, I have something like 50/100 Mo but I still see 1.28 Go in the project page.
Web download with all scenes : 19.1 Mo zip
Export project : 92.8 Mo zip
Project size in my project page : 1.28 Go !