Hi @darknight,
The short answer is no.
Journey uses Google Drive sync to keep your entries intact across all devices.
This means that your entries sync and download to each of your devices where Journey is installed.
As such, there's no way to reduce the amount of storage used on your device, as it's based on how much storage you use and choose to sync via your journal.
If you just want to use the web version, for example, then there's really no storage used on your device because the web version does not download your content to your phone. If you use the Journey app, it will download all contents, using storage.
For example, I have about 2,000 entries with many videos, equaling to approximately 7.7 GB in use. I sync a lot of content. It's really based on the user.
Hope this helps!