I, and every developer in my company have been running Linux in various flavours in XPS 15s for several years now; it works just as well as on any other device I've used it on.
I use an XPS 13 at home also running Linux (Ubuntu/Manjaro) and have no unusual issues there that I haven't also seen in my desktop.
Saying it doesn't work well in Linux is either bad luck with a particular model or just plain misrepresentation.
I think it's bad luck with a particular model for me, and I can't even put my finger on why, exactly. The wireless and graphics are really unstable, though. Many live USBs will not boot into a GUI mode.
It was really aggravating for a brief period, then I decided that I'd just relegate that machine to being "the windows box" and moved on.
That's unfortunate. Which model do you have? We use models from the past 5 or so years, all with Nvidia cards, the only recent issue we've had was with a new model that arrived yesterday and Ubuntu 18.04 didn't have a wireless driver, but quick connection over ethernet and an update fixed that.
You also have to switch RAID to AHCI out of the box (if it came with Windows) but it's otherwise been smooth sailing from there.
As for graphics, Prime/Primus/Optimus (which ever it is, I'm never sure) is an issue with all machines and not a DELL issue, Linux support, in my experience, for switchable graphics is just terrible.
The machine I'm on now (XPS 15 9560) has nvidia always on, I used it plugged in 99% of the time anyway, I'm running Ubuntu 18.04 for work.
Agreed on the switchable graphics issue. I think mine was compounded by a nouveau issue with this particular nvidia part. One fix I'd have been happy with would've been to have intel graphics always on. That matches what I do better anyway. But I could not find a stable way to do that.
I found that installing the nvidia proprietary driver and switching to intel mode kept it happily locked to intel, then there is a fix for intel graphics for Xorg (conf change) to stop tearing in videos like YouTube. Performance for things that use GPU rendering (like certain IDEs :() wasn't great so I switched back on Nvidia.
We are all in various states of Nvidia/Intel proprietary/nouveau drivers/modes here depending on personal preference but none of us have any real day to day issues (On Ubuntu 18.04 at least, which is our preferred distro).
I'll have to give that a try. Fedora's the (very slightly) preferred option here mostly because we're usually deploying to red hat stuff. But that is not a religion and would take a back seat to a working laptop. If the XPS15 worked at native resolution with good wireless, it'd be much nicer than my current linux machine.
A bunch of the Ops guys here run Fedora, I've heard it runs better than Ubuntu, particularly Gnome, but in the dev team we're debian so I've not tried running Fedora.
I tried initially Debian, but it didn't really work. Fedora works much better, didn't have any problems, and it's just the much better distro (a >10 year happy debian and darwin user)
I use an XPS 13 at home also running Linux (Ubuntu/Manjaro) and have no unusual issues there that I haven't also seen in my desktop.
Saying it doesn't work well in Linux is either bad luck with a particular model or just plain misrepresentation.