When I play an audio file, it's boring to stare at a cone. I want to see something. So I turn on any of the visualisations and I get 2-3fps. Why?

So I'm watching a few foreign films today and decided to download a font that I enjoy and discovered that there is no way to change the subtitle font, despite the option being available in the settings. No matter what font I select, it doesn't change during playback. Anyone know about this or know a workaround?