I'm in the process of downloading the game. But if you're using unreal, did you select create compressed cook packages in your project build?
Go to project settings -> Packaging -> Packing section advanced -> "Create compressed cooked packages"
It should help reduce package size.
Hmm, Im not sure, you mentioned using the starter content perhaps that's bulked it up a bit?
https://docs.unrealengine.com/en-US/Engine/Performance/ReducingPackageSize/index...
This might be helpful to you. :)