From 2009 and up to 2018 there are topics on many forums, including this one, that debate the operation of the DSG gearbox and "what to do at a red light". Leave it in D or switch to N. I hope this thread will answer this question so we don't get topics like this in the future.
The answer is: Leave the gearbox in D !
Here is the official DQ500 info from 2009:
https://www.motor-talk.de/forum/aktion/Attachment.html?attachmentId=745184
Page 14 you can read: