Long layover in Shanghai

I am a US citizen that will be traveling to South Korea for travel, but my airline has me stopping over in Shanghai for 15 hours going, and 24 hours returning to the US. Because I am a tourist and US citizen, it is not required that I have a visa for South Korea. It is my understanding that I can leave the airport in Shanghai (I'm flying into and out of Pudong International Airport) since my layover is less than 48 hours, and that I may stay in Shanghai without a visa. I wanted to verify that this is correct.