U.S. stock mutual funds started 2015 on a sour note, losing 0.26% as a group, according to Lipper Inc. data for the week that ended Jan. 8 — which coincides with the entire new year through that date. The decline came amid stock market news that fueled investor concerns: The global economy is slowing faster than previously expected. U.S. stock mutual funds notched a 7.56% gain in 2014. The week’s setback was the second straight weekly loss.