That's some thick stuff. You're welcome to use whatever you want, but every turbocharged vehicle I've played with (Porsche, DSM, Dodge Daytona, Saab, Audi, Chevy) short of turbo-diesels has a manufacturer recommendation for 5w30/10w30.

[edit] Oops, it's Mobil1 15w50. Typo on my behalf. [/edit]

[edit2] Under continutal severe driving conditions (high speed corning comes to mind, with long hard turns) a thinner oil would 'slosh' to the outside edge of the oil pan thereby offering less protection to the bottom end components. A thicker oil would help in a situation like this since it'd be less likely to slosh. And my 'continual' I mean the kind of abuse a dedicated road racing car would endure, where every time the car starts it's gonna get the crap beat out of it and not a straight quarter mile at a time. The occasional stunt a daily driven vehicle may run into doesn't really count.

For those of you in a colder climate (the northern half of the US) 15w50 would offer difficulties in starting. Trying to start 15w50 or even 10w40 in below freezing weather puts a lot more strain on the starter. For this and other reasons manufacturers typically recommend running 10w30 in the summer (thicker, more protection like what I previously mentioned) and 5w30 in the winter (thinner, easier for a cold motor to push.) [/edit2]

I'm off my soapbox now.