Shares of Yum China Holdings Inc. (NYSE: YUMC) were down 15.7% as of 3:15 p.m. EDT Thursday after the company announced underwhelming second-quarter 2017 results.Quarterly revenue climbed only slightly on a year-over-year basis to just above $1.59 billion, including 4% same-store sales growth at KFC and flat comps at Pizza Hut.