MichaelC[AP Moderator]
22442
While I have no absolute information, I would speculate
There are less than 2000 total Openworks produced at this point between the steel and gold models. It is definitely a limited production piece.
As for your other thought that 15305 looks like it wears larger than 39mm, I completely disagree. I have had it on a few times, in steel and gold, and to me it certainly looks smaller than 39mm. The reason for that is the minute track ring reduces the diameter of the openworked area, which is the "dial" of this watch (or lack there of).
Nonetheless, the 15305 is an astounding reference, but given your preferences for large watches, I am not sure it is the correct piece for you.