How can I change playback speed of mpv video player?

Are there shortcut keys to change the playback speed in mpv?

You need to refer to the Reference Manual:

The reference manual lists all the options and configuration options mpv understands, key bindings, scripting, and other customizations.

Use the following keys:

[ and ] Decrease/increase current playback speed by 10%.

{ and } Halve/double current playback speed.

Backspace Reset playback speed to normal.

Source: mpv.io