Setting a min wag at 50% higher than the next highest PPP min wage (Purchasing power parity) is a very risky move. In order to support it there has to be some combination of Seattle being better workers and Seattle being a more desired place to live. I dont see how anything over $12 makes any sense. If I am correct then this will not work. The way it will not work is that jobs vanish. There will be more black market jobs for sure now but since they dont generate tax rev they will not help much.
I have a feeling that this lasts two years, and the way it ends is a law passed in Olympia outlawing any municipality from variance from the state min wage. If this goes bad it is the States books which will get hard and fast, both will less money coming in because jobs disappear, and more money going out as the jobless line up for aid. Eventually property values will fall hitting the county and city books, but the state will have ended this experiment before they go down a lot.
Then the city and the state get to try to rebuild.