U.S. chief executive officers have become a bit more pessimistic in their outlook for the American economy in 2015 and fewer of them expect to increase sales, investment and hiring this year, a quarterly business group survey said on Monday. The Business Roundtable’s second-quarter survey, conducted before U.S. gross domestic product for the first quarter was revised down last month to show an annualized 0.7 percent contraction, found that CEOs expect 2.5 percent GDP growth this year.