Not only is it cool to honor David Kelly, it's also probably more useful to have a speed limit like 17 vs 15. The thinking is that 15 feels generic where as 17 is specific.
What? Those are completely arbitrary descriptors. I think 15 feels specific because it's a multiple of 5. While I don't know the history of using multiples of 5 as speed limits, I do know I'm easily able to tell when I'm driving at a multiple of 5 due to my car's speedometer layout.
I've heard this is the reason why Disneyland sets their parking lot speed limit to 14 MPH. I can confirm that it is 14 MPH. Never bothered to confirm that this is the reason why.