Jon, tried the BGE cast grate but it was 14.75 and a bit too big to fit down onto the bottom tabs. I found this on Amazon and ordered it due to the legs and it is 13.8 inSorry I couldn't get a reply to you sooner. But, yes, I was thinking mine was 15". I believe that is the correct size for a Medium Big Green Egg main grate.
I am very glad for you that you got one that works well! Will look forward to seeing your Duchess in action. I have been chatting with Mark Baron. He has already set up the Duchess grate as a "special order" item that you an order from his website. But, it is set up for the single purchase price of $150 plus shipping.
When my tax season winds down, I am going to make one last push on the PK and Duchess Facebook groups - and here on TVWBB as well - to see if we can at least get to 3, preferably 5. I didn't get a straight answer from Mark about making 3 or 5 at the lower price but then shipping to different buyers (including their shipping, of course). I am not going to ask again unless we get more interest.
If we don't get any more takers, then I guess we can each decide if we want to shell out the $150, plus shipping for a one-off. I am working on buying one from him for my "single-vent" small size Original. I couldn't get any serious response on the PK group for going in on this one. The "new" PK company used to offer a nickel chrome replacement grate for this grill but no longer does. I don't think they are real hip on promoting saving the really old PKs. I suppose understandably they want to sell you a NEW PK. They are a very good company, though, and deserve credit for bringing back the "Original" PK and developing the larger 360 model.