Chris, Ruth: as Onefin said, there is a lot of Sprinter discussion on the Sprinter forum he linked to, and it is a great resource for technical information about the care and feeding of Sprinters, including the 2015 and 2016 factory 4x4s.
That forum however, does not have much information about actually using Sprinters the way the Sportsmobile folks use their vans. As for how capable they are as a 4x4, there is very little out there yet. Those of us that have them are still getting used to them, I guess.
My wife and I have had our 2015 144" high-roof 4x4 Sprinter with a Sportsmobile RB 150 conversion since November of 2015. Our first 30-day trip in the van included 10 days or so poking around in Anza-Borrego Desert State Park and 4 or 5 more in Joshua Tree National Park. We took some baby steps into the 4-wheel drive arena, mostly in Anza Borrego. We drove some class 2 roads, and then worked our way up to a few class 3 roads.
I don't have much 4x4 experience, although I have a lot of 2x4 dirt roads behind me. The Sprinter did just fine on everything except for one crossing of a ditch as we exited a wash. I made a few attempts at a diagonal crossing of the ditch, and started spinning a rear wheel each time. Fearing I would dig myself in, I just backed off. With more experience, I will probably be able to handle that situation with some pressure on the brakes (says Alan at SBM west), but we were out there alone with limited recovery gear, so we turned around before we made a mess of it.
In May, we are planning a tour of the dirt roads in the Grand Staircase Escalante National Monument of southern Utah. We will stick to class 2 and 3 roads again, this time armed with more recovery gear. I will know a lot more about what it can do, and what our comfort level is after that. We're pretty cautious though, because it is such a nice rig and we don't want to scratch it.