I'm in exactly the same boat. You cannot disable MirrorLink in the S6 even under settings, because as soon as you connect the USB cable it auto switches back on. I contacted my local Lexus dealer and they had no idea - the comment was "sorry we all use iPhones".
This is really annoying, as i now cannot charge my phone whilst driving as i need info on who's calling etc from the mobile.
Anyone help please !!!
Thanks Len