Technically, it's from the spaghetti bowl to Lake Mead Blvd...for now. So if you were downtown and wanted to go to The Cannery, you could tour the ugly side of town to Carey or Cheyenne. Even if you plan out a seemingly good route, many other people who use 15 are looking for alternate routes too.
I never liked it and I drove on it once since I moved here. There's not much I want see and do in that part of town. The key to all freeway driving here appears to be timing, only the times and days of week differ from most cities.
I kinda like the surface streets as it gives me time to explore. I'm usually not in a hurry to get anywhere. With the exception of my route home from the airport on 215 to the Rainbow exit, I'd bet that I have less than 100 miles of freeway driving in town since I moved here.