Hi Theo,
Welcome to the Prismic Forum community, and thanks for posting! 
I'm happy to look into this and see how I can help.
For starters, you can see an overview of your usage in your Dashboard, at Settings > Usage Dashboard .
I can see that you work on wastberg.com. I took a look at the site, and saw that there's a short video on the homepage that is 8mb, hosted on the Prismic CDN. That could be the culprit.
You could try compressing the video (I think you could shrink it > 90% with basic optimization & compression), or you could host it on a dedicated service like Vimeo, Wistia, or Cloudinary (which is what we generally recommend).
If that's not the issue, could you give me the name of the repo in question? (You can send it in a DM if you don't want to post it publicly.)
Thanks,
Sam