Following a rapid expansion of luxury housing in New York City in recent years as developers took advantage of low interest rates, sales of high-end units have begun to slow, worrying stakeholders and raising concern over the health of the economy.In a coveted area along the southern end of the city's Central Park, a number of ultra-luxury buildings have sprung up or are under construction, including the 1,550-foot Central Park Tower, billed as the world's tallest residential skyscraper.Another building in the so-called Billionaires' Row features the most expensive home ever sold in the Uni…READ FULL ARTICLE