Hi CS, I don't know anything about AV515 glue, for a 12 string with the extra tension on the neck the Titebond is a small outlay or DB can send you enough for a small cost.
The thin strings in the thicker string nut slot will just buzz and sound terrible.
Try searching for a reverse 12 string nut or you could buy a blank and cut your own but would need nut files and a bit of experience