As 10 meters began its decline a few years ago, I would often ask AM operators if they ever used 15 meters. With very few exceptions, the answer would usually go something like: "No, because I never hear anyone else down there."
There was AM activity for a brief time around 21.400, and on 21.430. But, in casual tuning on the weekends, I have heard less than 5 AM stations on 15 meters within the past year. I say all that to ask just where is the "AM window" on 15 meters? And, why don't more of us operate there? Unless there's a contest, 15 meters is usually not crowded. Those of us who run rice boxes or similar power can usually hold our own there once a contact is established. Mike Duke, K5XU American Council of Blind Radio Amateurs