Yeah, 203e has very little carbon and about 3% nickel, while 15n20 has about .7% carbon and 2% nickel. Theoretically, the 203e should be a bit brighter in the etch than 15n20, but 15n20 will hold an edge and the 203e will not... I've used it recently in some composite blades where it was nowhere near the edge, mostly as an experiment to see how it looked. As the paper KenH linked says, if you mix it with a high carbon steel and fold it a few times the carbon content will equalize through the blade. This cannot be said for pure nickel, which some people use in damascus.
Admiral steel carries 203e (in 8 foot bars).