Last time I checked (which admittedly has been a long time ago), the speed limits of certain sections of the road between Duisburg and Calais were 50, 60 and 80 km/h.
By driving within these limits, players reduce the risk of accidents, maintain control over their vehicles, and foster a more realistic and enjoyable simulation experience.
Slow driving could only be regarded as blocking, if a player restricts
"a user's travel path, blocking entrances to highways or other entry points or anything similar."
(TruckersMP Game Only rules, §2.3 - Blocking).
I can't imagine a situation in which slow driving fulfills the elements of reckless driving.