$15/hr in Seattle at a fine dining restaurant? That's not as good as it sounds. If it were anywhere else, it would be fantastic. It's still a good direction, but it's not perfect. Here's why;
As long as you work at a popular restaurant in a more populated area, you can make $20+/hr as a good server. And there's pretty much no excuse to not be a good server, because it's just serving. I'm not saying working at a busy restaurant is the easiest thing in the world, because I'm well aware that it's quite stressful during the rush hours or busier seasons, but it's not difficult either. Honestly, the majority of the battle is just having a great attitude and being mindful of all of your tables. If you can do that in any situation, which you can if you're determined enough, then you can make more than $15/hr. Seriously, like, it's SEATTLE. Minimum wage in Washington is $9.47, but in Seattle? Like any large city, pretty much nobody pays minimum wage. Even in Tacoma, you can't find a place that pays less than $10, literally so long as you aren't working your very first job as a young teenager.
On the other hand, it's great news for everyone else. It's just terrible for servers for restaurants that go 'tipless'. I would quit being a server and work food prep instead. More reliable hours, less stress, same pay.
But really though, if you can't make more than that as a server in Seattle, then you are doing something wrong or you're working at the wrong restaurant. This is kind of nice because it's year round pay, but I can see it being even more of a reason to cut your hours when it's slow, just like everywhere else already does anyways.
With everything in life, it's important to consider other factors than just the one's presented to you. This may be a good thing, and it certainly is in some cases, but there's possible downsides to consider as well. Tipping is weird elsewhere in the world, but it's very lucrative if you're good enough or likable enough. Look at Twitch streamers. The more popular streamers make absolute bank and the bulk of their income from tips. And in a restaurant setting, I very honestly do believe it makes a difference in the servers, because I know that I work harder than I would like to ensure that I make as much as possible, and I'd venture a guess that most people feel that way too.
It really might be good for the economy to have more people with more pay, though... Perhaps they should make this standard everywhere. Who knows. Hard to say.