It would all boil down to fire control.
That technology circa 1940 versus even four years later, the technology on the Iowas was very different. If the Bismark had 1944 technology she would do well. The difference between a 15" and 16" is very slight. Certainly the 15" of the Bismarck showed what happens when that round penetrates into the ammo bunker. And, for those theorists who go with the 8" of the heavy cruiser Prinz Eugen actually took out the Hood, makes the case even more so. Rounds on target is what it's about.
Six to ten hits from the Bismark would leave an Iowa in rough, rough shape!
Boo