I just designed a Minelab Equinox Coil Ear Stiffener a few weeks back. Has side braces for extra strength and zip tie holes if your ears are already broken. Uses minelab bolt. Fits the 11". I still need confirmation it will fit the 15", but I'm pretty sure they are the same size.
PM me for details, I'm not sure how much more I'm allowed to say.
Pic of a prototype, actual ones differ slightly -- more beefed up.
Edit -- Added Tinkercad 3D image of my current design.