I have an adapter that would be ideal for the 15.
It wouldn't allow the 35 or 50 to focus, it has no groove for the focusing follower in the camera to reach the inner barrel of the lens.
I've never seen one without the cutout so I ASSUME it's for a visoflex which wouldn't need the cutout.
It's not listed in the Leica Accessory Guide 2nd edition and is marked "Zidem" and West Germany.
I'm thinkin' $25.00 shipped.