15% of billions is a lot. While the exact number of desktops is likely unknown, its safe to assume MacOS has several hundred million users. I'd suggest that as serious.

But it merely reflects my point that there tends to be one big player in most markets. Android / ios is also skewed (globally) but ios is very much a player.

You don't have to be number 1 to be in the game, but past number 2 it's very hard to break in. And if number 2 is strong, close to impossible.