For modern cars, just follow the owner's manual recommendation and you will be good even if you run 15-20min track and let the car rest.

Apex run 5W-30 for their Nurburgring rental car fleets. The tourist usually take a couple of laps each session.

For their famous M3 Taxi (that take tourist around the ring), and M4 (rented to Robert Kubica once, who ran it throughout the day) that have 15W-50.
The reason is on busy session the M3 will be fully loaded with passengers (2 bucket seats at the back), they would run it all day long and don't stop the engine between run.

Then for the super cars GT2 RS MR, the Mclaren, the Pista pretty much follow the owner's manual as well. They only run a couple of laps each time, and don't get stressed as much as the two M Power.

So there you have it, again follow the manufacturer recommendation.