My city does the interviews through a background check company and not at the airport, so it really depends. Sadly, we don't have the ability to get global entry here because there are only domestic flights from our airport I assume.
That said, at FLL, I had a huge pre check line but it still went much faster than regular because you don't have to take shoes off and remove things from your bags.
Last time I flew, there was only one person in front of me in the pre check line, but she'd gotten it free and never been through before so it took her much longer than normal to get through. I still can't explain why, but she somehow took almost ten minutes to put her bags on the belt and go through the scanner.
Frankly, that's the one reason I don't like random free pre check assignments - people who don't know what they're doing slow things down for everyone else who paid.