Proxies created from cameras have the audio shifted. The proxies that Premiere Pro makes does not really reduce the size as well as the camera made proxy can.
Jim Simon commented
The point of proxies has never been to reduce the size of media, it has always and only been to make editing easier. In the early days on NLE's, smaller files were used to make editing easier. These days, the files are difficult to edit precisely because they're so highly compressed. That often means larger files are needed to make editing easier.