After installing 50 rounds of new driver updates from Dell, I'm basically back in the same place with my XPS 15 and TB15 dock. I can't drive two 4K displays from the dock, using ethernet crashes the dock when Wifi is enabled, the NVidia card black screen of deaths the laptop, and the dock is generally unstable. I also can't boot with the dock connected.
I assume that everyone else is still having issues, too? It has been a couple weeks since there have been any new driver updates for the laptop or the dock.
Overall, I'm a hugely dissatisfied customer. I've wasted countless hours trying to get this buggy, defective machine and dock to work properly. I would be very hesitant about buying a XPS 15. With regards to the TB15 dock: DO NOT BUY ONE.