Are unused textures loaded from the folder into memory. If they are not stored in memory until they are loaded, does this mean that you can choose the quality/performance ratio using "set mesh texture"?

Babylon.js doesn't know about any textures you may have in your Construct 2 project folder until you use them with "Set mesh texture".

Currently the previous texture however stays in memory when you use the action. With the next update this changes and the texture will be disposed.