Good question.
Maybe he went 55 times to explore the Microverse because for each physical space, there's a different microverse.
As for the "very limited context given", well... I have the whole context. I read the book, I have the physical copy at home. So I have the exact context of the scene. The previous panels were of the Avengers saying they have to go to the Microverse because they had received a distress call that might be from Jan. Thor said he'll go, so did Steve, and Tony. Then Clint asked "Go where?" and Peter said "Hank is going to shrink us down so small we're going to be, theoretically, in a Microverse". Then Tony answered "Not all of us" (as in the panel I posted).