About the "Preview_Data" folder

When I make a build of my 2D desktop game, the "_Preview_Data" folder created alongside the executable is a whopping 774MB in size.

Most of the large files in the folder are of the "shared assets" variety. There are 37 of those in all: some small, several in the 20-30MB range, and a couple big ones (70MB and 150MB).

Is there anything that can be done to reduce these files in size?

About the game:

• All the visuals are quad-sprites, so there should be very little 3D data.

• Each level has its own scene file (34 levels total). Would it make a difference if I refactored the game to use only a single scene for all the levels?

• Unfortunately, most of the textures look bad unless set to "truecolor". They are sized to be no larger than necessary.

• I don't have anything in the Resources folder.

• Almost all the game objects are set up as prefabs.

If anything I'm doing stands out as a problem, or if anyone has general tips, please let me know. Thanks!