The Wifi speed on my Dell XPS15 is pretty bad.
Finally did a comparison test between the XPS15 and my old Vaio.
Tested upload and download speeds using my ISP test site, from the same location on my home
These are the average result:
DELL XPS: Download=9.80 Mbps Upload=10.94 Mbps
VAIO: Download=65.40 Mbps Upload=17.55 Mbps