When playing any compressed format, such as the Vorbis format, Wwise decompress the data in real-time during playback. It does not store it for later use.
Wwise will stream the file if the streaming option was specified in the Sound's properties. When the stream option is disabled, the compress data is stored in the soundbank and loaded in memory with the soundbank. However, when played back in Wwise directly, the files are always streamed. The stream option is only used in-game.
Please note that, for authoring purposes, when the Original button is ON (blue) in the transport, the original wav file (as imported) is used for playback. When the Original button is OFF (gray), the converted file is used for playback. You will then need to convert it before you can play it back.