Nikkei rises to 5-1/2-year high, exporters jump as yen slides

* Nikkei may reach 15,000 this week - broker * With USD/JPY assumption at 100, forecasts will rise 28 pct - analyst By Ayai Tomisawa TOKYO, May 13 (Reuters) - Japan's Nikkei share average surged to a fresh 5-1/2-year high on Monday as the weakening yen further bolstered exporters on hopes that they will raise their forecasts for the current year. Strength in Wall Street on Friday also spurred buying after some rosy earnings buoyed investor sentiment. The Nikkei rose 1.4 perc