Update: It took me a day to figure out what comment poster Louis meant by making it a streaming sound, but apparently there's a setting in the JSON for that: ""stream": true", with that added to the specific sound.. it works fine.

As soon you load a VORBIS sound file with a length around 3 minutes and a size of about 4MB by using the command '/playsound', the game freezes until its fully loaded and then starts to play it.