I've been testing the Irix 15mm with my Kipon Nik-FX Shift adapter.
This lens is great. very sharp, very low distortion. I have the firefly version, which is made of plastic, and the build quality is very good. One good feature is that it can focus beyond infinity, this is very useful if your adapter is not exactly of the right thickness. There is a click stop at infinity but you can go a little further.
One problem is that the lens doesn't have an aperture ring and my Kipon adapter doesn't control the aperture. (There is a Fotodiox shift adapter with aperture control). My solution was to insert a little bit of plastic next to the aperture tab in the lens mount. Now it's locked between f5.6 and f8. This is fine for my application but not ideal for general use.
I can shift up to 7mm, at 8mm there is a hard vignette.
