[Strugs]

Yes - the 5W seems to be everywhere, but no 15W to be found.

Service manager at the Porsche shop (not a dealer, just repairs) recommended topping up with the 5W until the next change then switching to dino oil 15W50 using the brand of your choice. He claims there is no advantage to using synthetics unless you want to run longer between changes. He also indicated that minor oil leaks using synthetic may disappear when switching back to normal oil due to larger molecule size.