This solved the very annoying problem with the docking station choosing the Dell monitor (usb-c interface) instead of the Thunderbolt-3 adapter (to my Thunderbolt 2 Display). In short, if it chooses anything but the Thunderbolt display first, it makes it so that the display will not work (oddly, all of the other things usb-wise (like keyboard, network, ethernet cable, and so forth), seem to work just fine).

General Notes

So, to make it choose the Thunderbolt display first, it's sort of a hassle, but here is what you have to do:

• unplug the Dell monitor (uses the large display port plug currently) -- this might work with a different cable adapter, but currently, I only have two usb-c ports and need both of them, so ... But, if you had additional usb-c port, then it would be worth a try.
• make sure that the Thunderbolt display is still plugged in (with the Thunderbolt-2 to Thunderbolt-3 adapter)
• turn off the laptop/reboot
• wait until it's completely booted back up and the Thunderbolt display is on and connected/working
• now, plug in the Dell monitor
• it should now work

You have to restart the laptop when this happens. I spent a decent amount of time trying to reboot the docking station, thinking that it was the order that the docking station hit the adapters, but it's not. It's the order of the laptop hitting the adapters that is important. You have to make it hit the Thunderbolt-3 adapter first, making that port (and all that are tied to it) think that it's a Thunderbolt-3 adapter, which (as per Apple) understands Thunderbolt-3 and usb-c. Go figure.