Really enjoying my Thinkpad x390, which is 13", but I'd easily go for a 15" version of this machine.

I had a 2016 Dell Xps 15" and both me and my coworker with the same machine had terrible issues with the keyboard randomly writing letters twice in a row. Also the on-board nvidia graphics card, while nice, was also a big power hog and that system had bad battery life until I turned it off. After a couple of years, the battery puffed up and started pushing up on the trackpad until it was unusable. Really soured me on Dell's build quality, and I can't recommend them at all, even though I admire their support for linux drivers.

Dell XPS 15, Thinkpads

XPS13 is very good for Linux but I don’t think I’d recommend an XPS15. Dell don’t sell them with Linux themselves.

You’d be better looking at the Precision line if you want a 15” Dell with Linux.

I think one of those or system76 will be my next personal laptop, but I hadn't seen any around the office yet (back when that was a possibility).

I haven't had an issue with Dell laptops.

Over many years, models, and indirectly hundreds of laptops (buying for teams, not myself) I'm pretty confident that Dells have a higher failure rate than many alternatives, but if you buy the higher tier support they are also more responsive than most. NB if you fall back on out of warranty and/or lower tier from them, support is not good.