First, the researchers at UW are looking at data to draw their conclusions, and posted their data and methodology (http://evans.uw.edu/policy-impact/minimum-wage-study) to invite criticism of their approach or conclusions as academics do with peer review. They concluded that so far it hasn't really caused any negative outcomes besides a reduction in the number of businesses opened.
Your mention of Planned Parenthood and babies is appropriate and shows how misinformed you are. The video is a fraud and used the same tactics to get footage as they did for the Godmakers anti-Mormon films. The guy who made the video about PP selling baby parts reported PP to authorities--investigators went hard at PP but there wasn't any evidence supporting the allegations, so they looked at the filmmaker who made the allegations. He's been indicted by a grand jury in Texas for racketeering for the video and is awaiting trial.
The 20.3% number for Walmart comes from their annual report. The number for Target is 20.5% (https://corporate.target.com/annual-reports/2015/financials/financial-summary). These are discount retailers with high numbers of employees and ar very efficient, and what other retailers would be striving for. Every publicly traded company prepares SEC filings and posts financial reports for investors and you're welcome to present something that shows different numbers.
Other people in this thread say that they're small business owners and would fire their employees if they were forced to pay more. Realistically, they'd raise prices and pass on the cost to customers just like every other business. It wouldn't hurt them too much since all their competitors are also subject to federal labor laws. The companies who'd hurt are businesses with no inventory and large numbers of low skill employees like landscaping companies.
Also, raising employee pay makes automation more attractive. Robots are getting better and cheaper, and they'll replace workers regardless of whether the minimum wage is $8 or $15--they will just replace people faster with the minimum wage at $15.