Is $15.00 per hour minimum wage inevitable?

Recently there has been a lot of talk and pressure to raise minimum wage in various states or locales.
Federal minimum wage remains at $7.25 per hour but most states already set their minimum wage above the federal.
Recently Portland, OR raised minimum wage to $15. for city workers.
Seattle is also @ $15.00 depending on the size of your company but for all companies it will be graduated in over time within a maximum of 7 years.
Los Angeles just passed legislation that will raise minimum wage up to $15. by 2020. After 2020 it will be linked to cost of living. Currently CA state minimum wage is $9. per hour. This raise would effect almost half of all workers in Los Angeles, nearly 800,000. workers.
NYC and Chicago are also considering such a raise.
Recently McDonalds under a lot of pressure agreed to raise wages on all it's company owned stores employees by $1. above local minimums, this will bring the average to about $10. per hour.