Set mouse speed on Ubuntu 16.04 on command line

xset m 1/2 8

You can experiment with these values. Thus, your system might be more suited to:

xset m 1/2 4

To reset default values:

xset m default

To make it permanent:

vim ~/.config/autostart/mouse.desktop

[Desktop Entry]
Name=Decrease mouse sensitivity
Exec=xset m 1/2 8
Type=Application
Comment[en_US]=Use xset to set mouse params
Comment=Use xset to set mouse params

Thanks to: https://www.pontikis.net/blog/fix-mouse-sensitivity-ubuntu