Read the info on the bottle. Oil containers have specs indicating their suitabilty. Spark combustion engines normally require an SJ or SH rating. These 2 are the most current. Your car could operate with an older rated oil, but none of todays quality oils have anything less that SH.
I happened to glance over the info on various "diesel" type oils awhile back and all were also suited for gas engine use as well. If you dig through the archives, you'll find more than one favorable mention of 15W-40 in gas engines.
1991 300-SEL - Model 126
M103 - SOHC
James Madison - Oppressors can tyrannize only when they achieve a standing army, an enslaved press, and a disarmed populace.
Liberty Firearms Training - After years of trying to regulate California criminals with a never ending stream of gun control laws they have still not given up with the belief that if they make something a crime that criminals will miraculously start obeying the law.