Nikkei breaks above 15,000 on Wall St; Sony untraded

TOKYO, May 15 (Reuters) - Japan's Nikkei share index broke above 15,000 and hit fresh 5-1/2 year highs on Wednesday, bolstered by a strong performance from Wall Street and further weakness in the yen. Sony Corp was untraded with a glut of buy orders after a proposal from an activist fund to list its entertainment unit sent its U.S.-listed shares soaring 10 percent. Its shares were indicated at 1,957 yen, up 4.3 percent from the previous day's closing price. The Nikkei rose 1.8 percen