On my C Class Mercedes, the factory fill I sadly put 13,000 miles. Now, I don't totally regret it. Mercedes (non AMGs) come with a break in oil, so I would have wanted to have it in there a good 8000 miles or so, but 13,000 I wish I had not done. However, that was the recommended OCI.
Now, I drive the car less and it gets changed about every 4,000 miles (1 year).