Yes, there are a lot of different factors involved when it comes to speed. In general, audio always downloads slower than video if the download is shown as a 50% audio/50% video download. So, in that sense, it is normal.
Please attach your StreamFab.log so that we can see exactly what was going on during the download. It is best to delete the old StreamFab.log first and make a new one with just one example of a download.
