If you use a set 3-4 angle seat cutter the 15 degree isn’t usually on them. I don’t think any of mine do. My best cutter is technically a racing cutter with a 70-60-45-30 and on Edelbrock heads I’ll hand cut a 15 with my Neway cutters. Many are only 60-45-30.
I understand. I wasn't trying to give advice, I wanted to learn if it could be fixed either by stone or cutter with 15 degree angle or if the seats are too far sunk to do anything with other than put new seats.