Is it possible to add 2 monitor to Dell XPS 15 Laptop?

Solution 1:

Yes you can, at least according to this forum thread (about two thirds down)

Relevant bit quoted:

YES, it is possible to connect two external screens to XPS 15. However, you need to disable the embedded laptop screen for the time being. You may NOT be able to configure it using your Win7 "Personalize" context-menu option nor by using keyboard but it can be easily done via NVIDIA Control Panel (use the checkboxes).

Solution 2:

you can easily connect two dell monitors to an xps15. I have two full hd monitors connected to my xps15, one by the HDMI socket and one by vga using a £10 displayport to vga adaptor off ebay which allows a standard vga lead to plug into it. Interestingly the displays are crisper than they were with my old laptop running the same setup. Window layout is fully configurable and I think you may be able to run laptop screen at same time as well if you really wanted to. Make sure you buy the right displayport adaptor as there are computers needing subtly different versions which do not work. Note I do not run my sound through the monitors.