More flexibility out of 15N20, and available in thicknesses better suited to fillet blades.
If you've never tackled a fillet blade, there are a lot of "twists and turns" in creating one. It's not bad forging the thickness, but grinding is where the frustration begins.
Generally when I produce a fillet blade, it's .050 for smaller ones, to around .070/.080 for those that are 10"+, that thickness means that the blades warp as they are being ground. Best practice is to have some type of a "backer" when grinding. There are a number of things you can use from wood to steel, but I prefer aluminum, because it "sucks" the heat away from the blade, and gives a measure of burning protection when grinding post heat treat. Correctly heat treating can be a bit frustrating too. Most of the time it's "Give-n-Take"..... meaning that personally the flexibility in fillet blades are more important to me than edge retention, so I will accept a bit softer than I'd like in order to achieve the flexibility I demand. Sometimes, that can be a matter of 15-20 degrees F when tempering. Hardening is also sometimes a real challenge. The first time I ever literally say a blade turn into a "U" shape in the quench, was one of my first 15N20 fillet blades.
Most folks who don't have experience with fillet blades think of them as just another blade to make/build..... but often learn that they are a very specialized discipline in knifemaking, and that there are reasons that you don't see many experience makers producing them.