I would expect the D-15 to be a stellar guitar, if it is based on the D-25. I have owned & played several D-4's, which were made in the '90s, and are very similar in construction to the D-25 (only at a lower cost). I'm not sure what the impetus was for the D-15, and for some reason, I'd always believed it to be made in the '80s. Never having seen one, I can't comment on first-hand experience.
But if the right one were to come along, I wouldn't hesitate to make it the right circumstances. While I have played a mahogany topped D-25 with a flat, and not archback from the '70s, I have yet to play a mahogany topped D-25, or a D-15. From my recollection, most people tend to really fall in love with them. Though they may be more sparse than some of the others.