If you care to, compare on Flicker what the UD and the 15mm do from side to side and corner to corner.
On the UD you have to choose which edges and corners you want to make sharp wehn focusing, if some are far and some close you cannot have all.
On the 15mm you can make it work for all corners and edges.
Either way one must look at the corners when manually focusing these old Nikkors. You can do it on any Nikon camera, heck, even the D3 had great live view for manually focusing across the frame.
