Wifi speed only 6Mb/s

Perhaps you could put your question to the ubuntu forums site -

https://ubuntuforums.org/forumdisplay.php?f=336

They will want to see the results of their wireless-info script. See -

wget -N -t 5 -T 10 https://github.com/UbuntuForums/wireless-info/raw/master/wireless-info && \
chmod +x wireless-info && \
./wireless-info 

This will download the script, make it executable, and run it, all in a row.