5 mb's on one object is quite a lot actually. But it's still only tiledbg - only on this you can set different images to different instances, so no collision mask, no image points, crop etc. And loading an image which is in 50% transparent is still waste of memory - transparent background takes more than solid color fill.
But I do see, this can be useful for some background stuff... I just remembered how much I miss "Load image from URL" in Tilemap object :/