As a Swede, Icelandic is a foreign to me as Finnish, meaning I don't understand it at all, in any way. Some words could be guessed, but that's the same for German too for most of us. Danish and Norwegian people I have no problem talking with though.

I might be biased with some exposure to Norse and Old English too, so I don't know whether Norwegians without that would recognise nearly as much (or little) Icelandic given how much Icelandic still takes from Norse.

I understand the western Norwegian dialects (/ nynorsk) have a much stronger old / west norse influence so are closer to Icelandic, maybe you are from those regions or are familiar with these dialects?

I'm from the east, but Nynorsk is required for all students (each region picks the main written language they want to use in schools, but also need to teach the other one), so we do certainly all get some exposure to Nynorsk as well and it certainly might help.