One of the recommendations we developed through the Dignity for All model national anti-poverty plan—which was a plan we developed in collaboration with a number of organizations, academics, and people with lived experience of poverty—was the negotiation of a living wage amount. We didn't land on whether that would be $15, but we said it would be a living wage that's indexed to the consumer price index, so that it could move throughout the years due to inflation.
On September 25th, 2017. See this statement in context.