I am also facing similar issues with my new Dell XPS 15 (9560) and did some research about resolving this issue. I did following
1. Update BIOS to latest version as of 24.05.2017
2. Update Killier wifi driver to latest version Version: 1.0.1028 from Killers website
3. In power management of the adapter setting I selected the option for Highest Performance
4. made sure there were no Channel overlapping between several wifi-router in my house (I have 3 in different floors)
What I observed was following
1. I observed very good performance with high end routers like Fritzbox 7460
2. The performance was bad with other older router (mainly o2 homebox 6431)
I measured this with my my old laptop (lenovo) and new Dell xps side by side. The signal strength was not great or excellent . The old laptop (lenovo yoga) never had issue with performance despite signal strength but the Dell XPS 15 had issue with performance.
But when I connected both the laptop to high end routers like Fritzbox AVM 7460 the connection speed in Dell XPS was almost on par or even better than my old lenovo laptop which uses Intel HD Wifi.
My take on this is that for some OLD routers the performance could be an issue for Dell XPS. I will once again try it out and post it in the forum. Let me know if others have seen similar observation ?
I also just got an XPS 15 9560, about 5 days ago. Pretty much since then, it has been disrupting my internet. I tried all of the things people have been trying (FYI I have an TP link archer C7 router). I called my ISP and they updated my modem settings, I reset my router and did a firmware update on it, I updated the Dell BIOS, and I also updated my Killer dnetwork card driver. I also did other things people suggested: changing my power mode to high performance, changing the killer network card roaming aggressiveness to medium-low. None of this seemed to really solve the problem. But, I found these two websites helpful:
After seeing the thread on the first website above, I decided to call Dell support, because why should I settle for an inferior network card on a brand new laptop I just got? I told them about the issue and he pretty much knew right away what the problem was. Apparently the new/updated drivers on the Killer network card (which comes with the XPS 15 laptop) are causing the wifi problem. So, he sent me an email with a link to download a previous driver for the Killer network card that will fix issue. He did assure me that it shouldn't compromise the speed or performance of my wifi. Here is the link to do that:
So far, I haven't had any issues. However, if it comes back, I will be calling them back again and demanding an Intel wireless network card to replace the Killer one.