Actually, there's far more negative impacts if the minimum wage is increased to $15/hour. Although what Sharke has pointed out above is the initial issue, many small business owners currently are not making 10% profit and this move will undoubtedly sink their businesses. Others will have to let people go and/or dramatically raise the prices on their products to cover the increase. $8 Big Macs anyone?
But, here's the bigger ripple effect that is not being seen yet: Joe currently makes 20% more than the minimum wage because [insert any reason here, seniority, tougher job, supervisory position, etc.] when, suddenly, John, a new-hire with no experience, is now making a lot more (Oregon and Washington already have some of the highest minimum wages at $9.75 and $9.47 - the highest is in D.C. at $11.50/hour while most are at $7.25). For the Pacific Northwest, current minimum wage earners would immediately get more than a 50% raise (without doing anything more or better). Obviously, at the very least, everyone who used to be making more than the minimum, but less than $15/hour will also have to be bumped up to the new minimum, however every one those people will now be screaming for an increase from there relative to where they were before (and why shouldn't they?). Needless to say, now some of those employees will now be making more than those in tougher positions or even their own managers so now THAT class of employee will demand a raise as well. And up the chain it goes.
It's only a very naive socialist view that the "extra" profits from so-called greedy business owners will now be spread out all the way to the lowest paid employee. The reality is that the truly greedy ones will never distribute what they consider to be "their" profits and will simply raise their prices to cover the new expenses (maybe my guess was low, $11 Big Macs anyone?). More and more businesses are already cutting employee hours so they don't need to provide benefits and this will only get worse. Ok, so the minimum wagers now make a LOT more (which, frankly, they don't deserve - read Sharke's other topic to see what the typical low-level employee will provide for that money), but they will now have to cover things they might not have had to before like medical, dental, any days off (which are now without pay), etc.
Anyone who thinks now that these lowest wage earners will now have more money to spend to make their lives better will find that they really don't after everything that they have to buy now costs more.
What about retirees? They've already made whatever they could in hopes it would last for the rest of their lives. Huge increases in the cost of living may mean they run out of money long before it's their time to pass.
There's (at least) one more impact as well. Anyone NOT working who's been barely scraping by will now be truly screwed since anything they've been making is not affected by the minimum wage increase so they now have far less money relative to what they need to get. Even those getting some form of government assistance will feel this since you can bet that all of them won't be getting a 50% increase in their benefits!