While I don't use unreal, I have noticed from other jams that the games made in unreal tend to be rather large, to the point where even a small game ends up with a multi GB download.
I know it's a very powerful engine, but I personally don't expect a small game that might only have 10 minutes of content to be multiple GB to download and play. Suffice to say I understand your pain in making a web build that meets Itch's policies in Unreal. Regardless of how you did it, you did do it though.