Shapton Pro 12 was 15 in the past, as said above. 2:1 stoneWhich 15k stone did you use? One doesn't hear of those too often.
There are some 15-16k stones out there. Not a very usual grit, though.
Anyway, higher grits are about skill before the grits themselves. Some stones might make it easier, some not so much. This doesn't make them better as in best possible results, but some results are better than no results or worse. And at some point you choose even without knowing. I do like some stones better than others, but that might be just me.
One of the most unusual combos is the Sigma 1200 + 13000. Seems so unreasonable to make such a huge jump and for some purposes it is, but for some reason, the 13k really improves edge retention even with more demanding alloys (like ZDP-189 or HAP40). I was quite amazed especially with ZDP-189. I always wondered how such a combo came into existence (since Sigma has 6000 and 10000 that would have been a more convenient choice maybe).
Not really true. Was proven already that micro fractures at apex level will dull the edge faster (even maintenance involved). There is something that concerned some alloys where the structure is so much more resilient, that would actually benefit, but rarely, if at all, common with kitchen knives.So I am going to respectfully disagree with you on that, coming just from an engineering point of view. When you have a “ toothy” edge you have a more structured edge, meaning the highs and lows of your grind add a structural rigidity to your edge it will last longer but may not get quite as sharp. When you go to a higher grit and start removing that structure you lose edge retention, for me that is just straight up engineering and geometry.