All modern factory-turbo cars use water-cooled turbos.
Synthetic oil's one big difference from Dino is it cokes instead of sludging. Without the water cooling you would still need to idle or get a turbo timer.
If you have been beating on it, let it idle a minute(ish) before turning off I guess. It isn't that big of a deal
2012 135i. dinan stg3 | ohlins dfv