UP2715K, Precision 15 5510, 5K3K?

The Precision 15 5510 only has the one Thunderbolt 3/mDP out port. So you will only get 4K2K 3840x2160 60Hz resolution.

The UP2715K ships with two DP-DP cables and two mDP to DP cables. To drive the 5K3K 5120x2880 resolution, the system must have two DP outs or two mDP outs to connect to the UP2715K DP #1 and DP #2. If the system has only one DP out or mDP out, then you can only get 4K2K 3840x2160 60Hz resolution. You should read through the User's Guide here.

I can't imagine that Dell would recommend purchasing the two together unless they actually worked together properly? Is there a TB splitter or some such thing that would make this work?

The sales site does not compare the monitor ports and specifications to the computer ports and capabilities. The sales site simply ships what you choose. You should contact Dell Customer Service and cancel the order for that monitor and select another model. I have never seen or heard of a TB3 splitter.

To be clear, it's not that I simply chose a monitor, and chose a computer, and then expected them to work together. The monitor is a *recommended accessory* when configuring the laptop. Before I chose the 1TB solid state drive, did I need to look up the manual for the laptop to see if it would actually plug in to the laptop?

I am simply stating the facts about the sales site and how it works. All I can do is email the marketing team and inform them of this issue. Doing so does not change what you should do, contact Dell Customer Service and cancel the order for that monitor and select another model suited to a computer with only one Thunderbolt 3/mDP out port.

I will certainly contact my rep, and have her send me new shipping materials to send this monitor back. Sigh.

What is confusing is that Thunderbolt 3 supports multiple 4k video out, which seems to be how this monitor works. The only issue here seems to be the internal monitor wiring not doing the obvious thing in daisy-chaining the two 4k monitor signals coming down the DP cable. This article is far from clear about what the hub will do, but perhaps it will solve this problem:

en.community.dell.com/.../new-dell-docking-solutions-help-improve-productivity-and-expand-connectivity-options-for-mobile-workers

Actually, I see that we have had a misunderstanding. The laptop has a TB_3_ connector, which is not a mini-display port, as you suggest above (seems to be confused for TB_2_). TB_3 is capable of carrying two 4k signals, which is plenty of pixels to drive the monitor. TB_3 also supports MST, which means they can be daisy-chained, or teased apart with a splitter, in theory. There don't seem to be any TB_3 hubs out yet, but they should provide the needed split. The question which remains is whether the NVIDIA graphics card (I seem to recall it's a M1000M; a rather complicated way of writing 3000, if I've ever seen one) can support the display. Is there a compatibility list somewhere?

The laptop has now arrived, and I am driving the monitor via a dell docking station which plugs-in to the USB3.0 port on the laptop, and gives a single DP out. I've done a colour calibration, and the thing looks great! But I can't justify the extra $1200 if I can't drive it at full resolution (and, frankly, from the NVIDIA graphics card to get a decent frame rate, rather than via the lousy intel chipset in the docking station).

Some more detail: the listing for the XP15 (sister laptop to the 5510) includes an accessory as 'coming in 2016' called the TB15, which is a docking station which supports dual 4k monitors. The TB15 doesn't seem to have its own page on Dell.com, but it is listed here:

www.dell.com/.../pd

I suppose we can just wait and see.

I have never seen or heard of a TB3 splitter.

I have found a Thunderbolt 3 to 2 DisplayPort adapter from the respected accessory company Startech. I hope you find it useful:

https://www.startech.com/AV/Converters/Video/thunderbolt-3-to-dual-displayport~TB32DP2

I am sure I will need it when the time comes to renew my laptop.