Yes, space can be saved by integrating 2D videos (not 360° videos) through an external web source – instead of uploading them as a media file. To do so, simply add an object and then insert the relating web link in the tab “external video”.
This way, the VR project does not load or store the files of the 2D videos – making the project effectively much lighter and saving space. Furthermore, please make sure not to integrate too heavy files in general. Try to reduce the file size of all your media assets (360° photos, 360° videos, images, icons, …) as much as possible beforehand.