There is no minimum speeds. The autobahns are nothing but highways and are the only way to get to different cities. Heck most of the autobahns do have a speed limit, which is 120 kph. Some areas are 130 kph, there aren't many areas where the autobahn has no speed limit. Most of the autobahns are always under construction, so you have to slow down a lot to 80 or 60 kph.
I have lived in Germany for over 8 years and have traveled on the autobahns with my Jeeps all the time. That is how I get from my house to the base everyday. This guy was not paying attention. The police found him at fault.