TB16 Dock Compatibility Help

As an aside, you seem to be using Mini DisplayPort and USB-C as interchangeable terms, and they are not; they are distinct physical connectors.  USB-C can send a signal that uses the DisplayPort protocol (if the connector has a GPU output wired to it, which not all USB-C connectors do), but be careful not to mix protocol and connector terminology.  The Latitude 7480 has USB-C connector capable of sending a DisplayPort signal (with Thunderbolt functionality as an option) and an HDMI connector; it does not have a Mini DisplayPort connector.

And just for future reference since you mention you're new here, with respect to your comment that you bought a TB16 "hoping" it would provide more display bandwidth, you'll be better served asking questions here BEFORE you purchase reasonably expensive equipment.  As it happens, the TB16 you bought will in fact work with those systems to achieve your desired goal, assuming the 7480 has Thunderbolt, but it sounds like you got lucky there rather than having arrived at that decision after understanding all of the technologies and factors involved -- and USB-C and Thunderbolt definitely have their complexities especially since not all systems with USB-C and Thunderbolt have the same capabilities.  If you'd like to learn more about how USB-C and Thunderbolt work, though, I wrote a thread about it here a while ago that you may find interesting: http://en.community.dell.com/support-forums/laptop/f/3518/t/20017807

Thunderbolt is optional on the Latitude 7480; the default configuration is just regular USB-C with DisplayPort Alt Mode, which provides only enough bandwidth for a single 4K @ 60 Hz display and even then only when the USB-C port is being used SOLELY for video output, e.g. through a basic USB-C to DisplayPort adapter. If the device connected to the USB-C port also wants to handle USB traffic, as would be the case with a dock like the WD15, then regular USB-C only provides enough display bandwidth to properly run a single 4K @ 30 Hz display, which is why you get a fuzzy result when you try to drive a 1080p display on top of your 4K display through the WD15.

Thunderbolt by comparison can handle dual 4K @ 60 Hz displays while also carrying other traffic -- but again, only if your system has it.  To check that, go into your system's BIOS and find the Thunderbolt Settings area.  If the options are configurable, you have it; if everything is grayed out, you don't.  If you have Thunderbolt and things still aren't working, make sure you have your system BIOS, Thunderbolt software/driver, Thunderbolt firmware, and graphics drivers all installed and updated.  If you don't have Thunderbolt, then the TB16 won't work at all, except maybe to charge the system.

I appreciate the quick and prompt feedback. It was very helpful.

@jphughan sorry for the confusion. I meant the USB-Connector on the side of the 7480 which I use to connect to the dock. That port appears to have the mini-DP symbol instead of the lightening bolt. Sounds like I am out of luck running the 4K at 60Hz using the Latitude and docks. I got a great deal on the TB16 and new it would come in handy with the XPS 15 and 12 which have Thunderbolt ports.

Since the TB16 won't work with the Latitude Is there a way to direct connect the Latitude via HDMI to the 2715Q? Not sure if it's a higher bandwidth 2.0 port.

Thanks.

Oh, so the non-Thunderbolt 7480s have a DisplayPort logo there? That must be to indicate that the USB-C port supports video output since that isn’t mandatory, but I can certainly see the confusion that would cause.

The native HDMI output is only 1.4, unfortunately, so unless you’d be open to swapping for a 7480 that has a Thunderbolt (you could at least perform an image backup to migrate your system over to minimize the time penalty), your only options for getting 4K @ 60 Hz are a USB-C to DisplayPort adapter or USB-C to HDMI 2.0 adapter, although either of those would preclude the use of a dock and also require an AC adapter to be connected separately to charge. Technically you could also look at the D6000 dock, which will do triple 4K @ 60 Hz over regular USB-C or even USB-A, but it achieves that through the use of a DisplayLink chip rather than having the displays natively driven by the GPU (even when using USB-C), and that has side effects and limitations you may not want. I can go into more detail if desired, but also note that the D6000 wouldn’t provide enough power over USB-C for your XPS 15 the way the WD15 and TB16 can.

Unfortunately there’s no single solution that would work with all of your current systems and displays. Sorry!