Your BMW dealer carries two versions of Advantec motor oil
15W-50 semisynthetic intended for use in air cooled boxers such as Oilheads, Hexheads, and Camheads.
5W-40 full synthetic intended for use in Wetheads and any other model with a wet clutch.
It’s apples/oranges comparing wet clutch bikes to auto style clutch bikes as regards motor oil. In addition, aircooled motors are different than water cooled motors. (All BMW with wet clutch are water cooled.)
Nothing wrong with using a full synthetic in the older aircooled bikes, but it’s still probably best that it’s 50 weight, as surely aircooled motors feature larger clearances. The W number (first number) of any oil is essentially irrelevant unless you intend to start your motor in arctic conditions. Even then, when I once read some Mobil 1 specifications, 0W,5W, and 10W all featured the same cold pour point. That is minus 55 F, btw, so again ... irrelevant.
It’s fairly critical to use the 5W-40 full synthetic for best wet clutch operation.