How long are you going to keep it? If under 100,000 miles, just go by MB's 20K schedule and spend the savings on fun stuff. If you're going to keep it forever (or do your own oil changes), I'd probably do 10K normally and maybe 3-5K for the first change.
Diesels have much bigger oil sumps and tend to be built to take a lot more abuse. That and diesel oil changes cost a heck of a lot more (especially if paying a shop) so if the engine already lasts 300K with 20K intervals (which they do all the time), you will have saved enough in oil changes to buy and install a rebuilt engine.
When I had a freight company I got into retrofitting bypass oil filters and doing oil analyses to determine change intervals. These were all Detroit 12.7s which I believe were spec'ed with 15,000 mile intervals. Anyway, I'd plot the wear metals vs miles or vs hours but the shapes of the curves varied dramatically from truck to truck. Then because each truck had a unique fuel card I plotted wear metals against gallons of diesel consumed and I'd see that the wear metals would do a slow linear increase until about 3,000 gallons of diesel at which point the curve would shift and it would start wearing faster. Some trucks got 5mpg, some trucks got 8mpg. Some trucks drove city routes and had higher hours per mile, some guys did express long hauls with relatively low hours per mile. But when they'd burned 3,000 gallons of diesel, we'd know it was time to change the oil.
And all the engines lasted 750K to 1.2 million miles which is pretty typical for the 12.7, but in their lifespans they all pretty much used around 150,000 gallons of diesel. So if you were going to bean counter costs, I'd go by fuel rather than miles...