I just got an email response from Will Shortz, crossword editor of The New York Times, on my second submission:
"Hi Christian,
"This is Joel F-------, writing on behalf of Will.
"Will says thanks but must send his regrets on your 15x. The theme is solid, but it didn't interest him quite enough to say yes.
"Sorry about that!
"He did appreciate the chance to take a look at this, though."
That was not the most useful feedback I ever received, which is why I'm soliciting yours.