First I'd like to say that I have searched a lot and tried many things to solve my problem. But nothing seems to work.
I have a Dell laptop Inspiron-5448 with Ubuntu 14.04. It is new and Ubuntu came pre-installed. My wireless card is Intel Corporation Wireless 7265 (rev 59).
When I connect the LAN cable from the router to my laptop, the internet works with 30 Mbps. When I'm using WiFi it goes as low as 2Mbps. Sometimes even less. Other laptops with Windows and even with Ubuntu 14.04 have no problem.
I don't know what to do anymore. I hope there's someone here with enough knowledge to find out what is happening.