I've got a Precision 5510 (updated with the latest 1.2 BIOS, thunderbolt updates, etc.), a TB15 dock, and now the UP2715K monitor. Unlike others who couldn't get things to run, I think the latest drivers and BIOs have fixed most issues. I'm still seeing major issues though:
* Most of the time, when I dock the laptop, the monitor shoud half the screen very clear, and the other half is "split" vertically into two, and the two sections are swapped. So, if the screen image is divided into four sections: A-B-C-D, then I would be A-B-D-C or B-A-C-D. Sometimes, the furthermost "wrong" part moves rapidly left and right by 100 or so pixels.
* The only way to resolve this seems to be turning the monitor off and on (by yanking power).
* After a few attempts, the image corrects itself, but there's a major flicker. If the monitor is left on, the flicker reduces in in tens of minutes, it goes away.
* If the monitor is turned off, and on, there's always this flicker. Even disconnecting all cables, and running monitor diagnostics (via button 1 & 4), I see flickering. During the diagnostics, I see White (heavy flicker), then red (no flicker), green (no flicker), blue (no flicker), black (no flicker), white (no flicker), the a screen with diagnostic text on the left and right. One of the texts flickers, but the other one doesn't.
I've had the monitor replaced, and the new one presents the same symptoms. I've connected the dock to the monitor with a single miniDP cable (4K), and also via miniDP->DP + second DP cable (all cables came with the monitor) for 5K. Regardless of 4K, 5K, or lower resolutions, the major distortion on connect, and flickering issue presents itself.
I haven't yet been able to test the monitor without the dock. I'll be able to do so on Monday when an HDMI -> miniDP adapter arrives.
My question is - is this a monitor problem, or a dock problem? Seeing that the monitor flickers on connection when the dock isn't connected, does it mean it's a monitor issue? If so, how are two monitors suffering from the exact same problem?
The TB15 dock has major issues. You might try turning off switchable graphics and powering the laptop w/ its own adapter and w/ the TB15 using its own power too, and attaching nothing else but monitors. This seems to have gotten in my case, all three external monitors working.