Let's be more specific.

Sushi Ginza Iwa and Sushi Iwa 815 are two separate restaurants. And to further add to the confusion, there is Iwa Hanare.

od_sf is talking about Sushi Iwa 815.

TWA884 Is talking about Sushi Ginza Iwa.

I myself have been to Sushi Ginza Iwa and can recommend it for lunch, though it is not my favorite experience. I prefer a longer meal at Sushi Shin in Nishiazabu (about 12 min taxi ride from Tokyo Station), if you can do the dinner, just due to the interaction and watching the preparation.

OP, unfortunately many top-end sushi places are closed Mondays.