$15 now is all about demanding everyone get the same [minimum] wage, but demand they work. Its communism. It hurts business, and it hurts capitalism in general as it shuts out market forces.
Giving *everyone* a set amount of money. Rich and poor, just enough so the idea of absolute destitution is no longer relevant. At this point, employees can negociate their own wage, so we can drop minimum wage. Some businesses can get away with paying less, if the job doesn't deserve paying any more..(for example, does a deck chair attendent, really deserve $15 / hour???). Result is businesses start paying the rate demanded by the market. not by the government.
To give a good metaphor, consider an electronic amplification circuit, with a transistor, capacitor. and a *resistor* to provide base bias. Because a transistor only works when current flows one way, if you feed a transistor an AC signal, it will only work 1/2 the time.... So, you add a resistor which provides a bias voltage, so the AC signal is raised so it never drops below zero. This makes it work all the time.
Basic income acts the same as this 'Bias' resistor... it provides just enough so that a persons income/outgoings (excluding savings) never drops below zero.