I have my original unflashed ECU in my 2015 SL. I get a little hang but it's not all that bad and I can live with it. Always scared to mess with something that works, I have no steering issues or dead spots. If the flash will cure the hang maybe I'll flash it when I bring it in for the headlight wire recall.
I agree with you, mine has never been flashed either, i also have a little hang time on the rev sometime. It is not something that I worry about.