The seemingly insatiable appetite of companies for their own stock is unlikely to be satisfied soon, even if the U.S. Federal Reserve begins to hike benchmark interest rates and shares get pricier. Buybacks may lift earnings per share of companies in the Standard & Poor’s 500 index by between 1.5 and 2 percentage points this year, according to estimates from Voya Investment Management in New York. With earnings estimates now calling for 1.5 percent growth for all of 2015, buybacks could make the difference between positive and negative growth in S&P 500 EPS.