I've found the wifi slow and not particularly stable with this on Ubuntu 15.04 on a new computer.
I have FTTC internet. Using the computer on wifi with Windows 10 or on a wired connection on Ubuntu I get dl speed of 70+meg. When using the test at www.speedtest.net the dl will start very slow and gradually speed up to around 10meg. However, in actual use I'm lucky to get 1meg. When updating Ubuntu it slowed to a halt and I had to switch to ethernet.
With ethernet and wireless both connected it slows to unusable.