I know you stated this is an inaccurate in real life and only in video game slowest but in actual NBA combine results, some big men like Shaq, DeAndre Jordan, Dwight Howard, and KAT had faster 3/4 sprint speed result than some guards. Shaq and DeAndre ran the 3/4 sprint at 3.25 seconds which was the same result as guys like Chris Paul and faster than Damian Lillard who ran 3.33 seconds, which equaled KATS result at 3.33 seconds. Howard was a freakish athlete who ran in 3.14 seconds, close to John Wall's 3.10 seconds. In the actual video games player's attribute for speed they would have guys like Shaq with a 50 something rating compared to Chris Paul who has a 90 something in speed in 2k18, which is totally inaccurate considering they are actually the same speed. I kind of wish the 2k series can be more accurate with the attribute numbers to make the game realistic so I basically edit the speed and vertical attributes by myself to make the game more realistic. And if anyone is interested they can find the players combine results on websites such as NBA Draft.net or Draftexpress.com and edit the players attributes themselves for better realistic gameplay.
Howard is extremely fast for a center, Yao Ming isn't even that slow. I'd say that the slowest will be Shaq, and current slowest would be Andre Drummond if you used him.