I'm from the UK, and as you probably know, Anthony Joshua is colossal over here. Even people who wouldn't watch boxing know who he is. really interested to know what his exposure and popularity is like over there, and how many people actually watch his fights on Showtime
People really have no idea who Anthony Joshua is, I think he got built up really fast in the UK and he never was exposed to the United States. The casual fan (not boxing, sports) in the US knows Mayweather, Pacquiao, then Klitschko. That's really it. As far as boxing fans I think people know guys like Ward, Kovalev, and Golovkin a lot more than Anthony Joshua.
People really don't care about boxing in the US anymore, it will change once you have a Foreman, Tyson or Dempsey come in.