Like everywhere, mom and pop businesses might feel a negative impact. A major amount of (mis)information on $15 has been successfully promoted by https://gspp.berkeley.edu/centers/cepp which is a think tank run by Cal Berkeley, and has a major influence by pro-Union, pro Democratic views. Nothing really wrong with that, but their work tends to get cited authoritatively in the media and adopted as public policy in Seattle more or less automatically without any peer review.

Source: A person close to me is studying social change and public policy, and a lot of the source material on $15 all kept being "non peer reviewed" papers and documents, and a surprising number quoted Cal Berkeley Goldman almost verbatim. This was interesting as her project was attempting to find peer-reviewed studies on the effects of $15, and there quite literally weren't any.

So what you can look forward to is some non-studied and overly promoted impacts, which will wind up hurting some business sectors more than people say they will, which the pro $15 people will then put down to unrelated to $15 an hour.

The whole reason unions are so pro-$15 is their contracts tend to be indexed off of the minimum wage, and if the city or country adopts $15, their membership gets X dollars added on top of that. It's a neat way to get more pay without having to re-negotiate for it. In a way I say kudos, nice strategy, but in another I hate seeing the fervent support for $15 that is either dishonest or not really up front about it's true motives. Based on opinion piece writing from a think tank that can claim academic sponsorship, but it turned out is providing very little in peer-reviewed source material.

Seattle's own city government's $15 an hour project paper released by the City quoted Cal Berkeley exhaustively. A non-peer reviewed source, basically a lefty think tank, is what is driving Seattle policy. Unreal to me, but here we are.