I started a thread on this down the page back when it was $400. And a gaggle of nattering nabobs of negatism said there's no market for a comeback of this machine. Horsefeathers!
HP, want to make some money? Bring back a revised 15c!
I think that one reason for the demand for this calculator is the quality and ease of use. I doubt that there would be much demand if a "new" 15C was built to the standard of the current 12C. I use an old (circa 1985) 12C, and have looked at a new one, but it is of substandard quality.