I too have been struggling (and pulling my hair out) with the XPS 14z WiFi issues everyone seems to be experiencing. Here is a temporary solution that took care of it for me last night and is still working as of this morning:

Press Ctrl + Alt + Delete.

Open Task Manager.

Click the Processes tab.

Select the Intel Wifi line then click End Process in the bottome right.

Once the Intel process was shut down things seemed to be working better for me.

One other tip: In Control Panel, I set the battery performance for WiFi to maximum performance on battery and when plugged in. This may help too.

Good luck everyone. This whole situation is very unfortunate for all who purchased this laptop.