RE: New XPS 15, 9530 WIFI issues.....
Just posting to say that I had a similar issue as the OP with my xps15 9530, and option 1 (update drivers) from your answer solved it.
I have the low end version (onboard graphics, 1920x1080 res, etc) I was getting about 3.5 Mbps download on my WiFi, while my android phone was getting 30 and my ethernet connected desktop was getting 90. This was on the stock wireless card drivers (v16.5.1). I went to the intel site and used the "check my machine for what hardware and driver version I have" tool (link), which worked and gave me a link to install the newest (v17.0.2) drivers. After the update I'm getting about 70Mbps down, which might still not be as good as it could be but I'm happy for now.
Note that when I did "check for driver updates" from windows device manager it thought that v16.5.1 was current, not sure where it gets it's info but I've always found that service to be hit or miss.
Also worth noting that I didn't interact with Dell support in fixing this issue, I usually don't involve them until I'm confident that I can't fix a problem on my own, or I need some hardware replaced or something.
Thanks again for the answer.
Edit: apparently replies always reply to the OP, I'm referencing Kaborchers' answer.