Mr Anduck's webpage says that there're only 16 of the 25's of 2015 edition in existence.
Yes correct:
2015 Titanium N Series Bitcoin Block
Unredeemed: 13 (81.25%)
Redeemed: 3 (18.75%)
Total: 16
In my opinion, the collectors who bought and held those 25's are strong hands and I can't imagine those pieces seeing the light of day.
Good luck!