My Internet connection is painfully slow and irregular on elementary OS Loki.
I'm connected to the Internet via WiFi through a PCI antenna.
What I experience is that I get disconnected from time to time, also the indicator shows a weak signal, but I just restart the connection and it shows a strong one again.
Trying to download from the AppCenter or using apt-get install is horrible. Right now I'm downloading the openjdk-9-jre, is a 183 MB download that is taking from hours to days according to the Terminal. This same download on my Windows partition would take from 15 to 25 minutes top.
I tried to use Popcorn Time and the Internet connection kept slowing until reaching 0 kbps, then I would restart the connection, it would comeback up and then down again. Using Transmission for torrents gets me the same result.
Strangely, I can browse the web and watch stuff like YouTube normally.
None of this issues happen on my Windows 10 partition, and they didn't appear while using elementary OS Luna or Freya.
If you need any Terminal input, just let me know.