Solved, it was an option in the My Dell software, under Presence Detection.
Hello, I recently purchased an XPS and while setting up I've activated a setting so that when I do not look at my screen it dimms the screen brightness and makes the PC go into sleep with an "AI" setting, if I remember correctly I've set it up at 60 seconds, I also think that it is a Windows setting and not a Dell one. I just find it inconvinient and I wish to desactivate it or make it in a longer delay. I tried to find solutions but I didn't find anything. Please help me and, Thank you.  
XPS 9315 AI Setting