For economy of your artwork count, mount several smaller pieces to one large artwork, with an image editing software, prior to creating your virtual artwork.
When you space the single works and give the gaps transparency when saving it as a .png, you will have the wall color show through in the gaps. (Check transparency in the 3rd tab, 3D display options). This will appear as ‘one artwork’ and thus also economize the loading process.
The downside: you do not have the information panel for each artwork but only the group, and the 3D effect is lost in this setting.