Here are some numbers to help you put it into perspective.
During the glory days for TLC ratings when LPBW was the lead-in for Jon and Kate Plus 8 on Monday nights, the Roloffs often drew over a 2.0 for regular episodes. The highest rated LPBW episode ever was the episode in Season 3 centering around Matt Roloff's DUII trial. That registered around the 3.3 mark.
The episode focusing on Mike Detjen's death received a 2.4
The ratings had begun to decline in Season 4 and saw them drop even further in Season 5. Many episodes came in around the 1.3 mark. Shortly after that, (after Matt Roloff had announced in TV interviews that the show would continue for at least 2 more years), that was when TLC made the decision to cancel the series. Some episodes of Season 5b came in around 1.1 and one episode failed to reach the 1.0 mark. The 1.3 average rating continued for most of Season 6, with the big exception being the final episodes billed at the "Series Finale". The finale got a rating of 2.2.
The first LPBW "special" since the cancellation that aired in Oct 2011 received a 2.0 rating.
Now this most recent special, the 2nd special so far -- received a rating of 1.5.
So a drop of 0.5 since the first special, but still slightly above the 1.3 average the show was receiving when it was determined that the show would be cancelled.