Fifteen thou is pretty tight. What I'm talking about are the M98s with the clip guide ground off with a body grinder. Nothing fits it. If the front ring is pretty straight with the bore, fill the gap in the back with black epoxy. When it's set, the mount is straight and can be cinched down without bending.
Japs are low on the front ring if they've been ground. Reverse the index surface and do the same thing.
If you want a 15MOA one piece, shim the back and glass both ends. It makes a no bend mount with an angle to it. The green stuff would probably work well on those.
Green bluing is somehow contradictory, don't you think.

Why are black berries red when they're green?