Ratings for Tuesday's Democrat debate: 15 million; ratings for the first GOP debate was 24 million. What does this mean?

In view of the fact that there are more registered Democrats than Republicans,  the only conclusion one can draw goes to the enthusiasm levels of both political parties.  Not looking good for the Dems.  

Understand that if one viewer shares his/her opinion to 10 other non-viewers.  the initial advantage,  such as it is,  goes to the GOP.