I'm glad you said that, after I posted my comment I got to thinking much the same thing.
Woah! We're agreeing on something in this thread! Best back up and resume our battle
That is kind of the point of the discussion, so just stating the case under discussion as if it were a done deal isn't really on...
The counter point is that if wages jump from ~$7/hour to $15/hour the payroll costs double and that has knock-on effects. I suspect a lot of companies can't afford to double their payroll costs and survive. Some can, some can't, but to assume that all companies are alike isn't helpful. The huge companies like Wal-Mart and Amazon would probably find it easier in theory (willingness aside) to increase the wages to their staff. Small companies don't always work the same way, and when you're dealing with small companies where the owners go without a salary at all some months because they basically get what's left over you'd be looking at shutting down those companies overnight. Is it better for a worker to get $8/hour and keep their job, or be guaranteed a minimum of $15/hour in their job but lose their job along the way and get nothing?
If you're talking a huge multinational then I agree it's more likely that they could pay $15/hour even though doing that would massively distort the market. Small companies, startups, mom-and-pop companies, may genuinely not be able to pay $15/hour for hired help. If a small company is forced out of business because the law mandates that the payroll costs double that also has knock-on effects. If the owners took out loans to start the company and the company has to shut down pretty much overnight the owners (who are likely to be couples, rather than billionaires) potentially lose their homes. This is just another problem with centrally mandated wages - the huge corporations can just hire a few extra administrators to sort it all out while the really small companies get crushed by the increases and the increased cost of compliance. And if you introduce legislation that only relates to companies with more than a certain number of employees it distorts the market around the defining line - if companies with more than 50 full time staff have to pay twice the hourly rate what do you suppose will happen in a company with 51 full time members of staff that doesn't want to see their payroll costs double?