A CONSTRUCTION crew in the south-central Chinese city of Changsha has completed a 15-storey hotel in just six days. If nothing else, this remarkable achievement will stoke further complaints from American economic pundits that Chinas economy is far more accomplished than ours in tending to such basics as construction. Meanwhile, its easy to imagine the disorientation of Changsha residents whod gone away, or who just hadnt recently ventured into the downtown neighborhood of the new Ark Hotel: Honey, I dont remember a hotel there, do you? The work crew erected the hotel - a soundproofed, thermal-insulated structure reportedly built to withstand a magnitude 9 earthquake - with all prefabricated materials. In other words, a crew of off-site factory workers built the sections, and their on-site counterparts arranged them on the foundation for the Ark project. YN