1095 is a 10XX series steel and all the 10XX series are shallow hardening, I cant remember where but I recently saw a thread where 1084 was referred to as deep hardening, and couldnt figure that one out. All of these steels have a pearlite nose that requires less than 1 second to beat, and that is about as shallow hardening as it gets without losing the Mn and going old school. Which brings me to my next point, many ancient swords were in fact water quenched but they were made of the simplest iron-carbon material you could imagine thus water would work quite well since very little else could cool fast enough to avoid making pearlite, but virtually every modern steel, no matter how simple, has manganese. That manganese increases hardenability and has been the frustration of many a swordsmith who treated 1095 or 1084 as if it were tamahagane and ended up with pieces in water quenches.
The 10XX series is designated as water quenching because in heavy cross sections used by industry the only way to through harden it is to quench it in water. However in sections of ¼, like a knife blade, it can be serious overkill. A successful quench has little to do with screamin balls hard as there is a maximum hardness achieved by complete martensite conversion and beyond that there is unnecessary stressing of the steel that will result in micro-fracturing, distortion and brittleness. The idea is to get as much martensite as you can with the gentlest quench that will accomplish that.
Shallow hardening steels will have a maximum depth that they can harden to with a given quench speed, and since a knife blade cross section is a wedge it has a varying degree of thickness and this is what causes a natural hamon to form when a certain distance for the edge exceeds the thickness the quenchant can overcome. Here is what I have observed with oils in a 1-1/8 wide blade ¼ at the spine and tapering all the way to the edge:
Slow quenchants (low temp salts, motor oil etc
) will harden to perhaps ¼ from the edge with mixed pearlite in the martensite.
Medium speed quenchants (Parks AAA, ATF etc...) will harden to perhaps 5/8 from the edge with mixed pearlite in the martensite.
Fast speed quenchants (Parks #50 and other fast oils) will harden to perhaps within 1/8 of the spine with pearlite mixed in the martensite only near the top of the hamon.
Water will of course harden such a blade all the way to the spine but with the speed to through harden ¼ the 1/16 edge will be shocked perhaps to the breaking point; ever notice how water quenched blades tend to crack at the edge?
All of these observations are based upon an austenitizing temp below 1500F and adjusting that temp will profoundly affect hardenability. The only thing that I would say is wrong in your approach is your soak temperature. 1550F is much too warm for 1095. The more carbon present the lower you want to keep you soak temperature. 1550F will increase hardenability to the point that you could get away with oils, and will definitely make water a very hazardous choice. Increasing the soak temp that much with .9%+ carbon will get you retained austenite and possibly grain growth.
Proper soak temperatures for 1095 are from 1475F to 1500F, with water hug the low side.
