Don't forgot more jobs being sent off-shore to a lower wage country.

Right now it might make more sense to pay a high school student $11.40 to do a fairly simple job rather than contracting that work out out to someone in China or India (or wherever) for $5/hour.  But if that high school student now costs you $15/hour the contracting out still only costs $5/hour the calculation starts tilting toward the latter.

Apply that throughout the economy and and all levels (as you note the person earning $15/hour now will want more) and you can easily start seeing more jobs being contracted out to lower wage countries.