On D1 you are suppose to "complete as many rounds a possible in 20 minutes" - so strictly speaking there should be nothing holding you back! After all, you are concentrating more on the cardiovascular on D1, so the more rounds, the better. (in other words, as fast as you can)
D2 is more for building strength and form, so your current approach for D1 should rather be applied on D2. (in other words, more controlled)
I see others have posted 50+ rounds for this workout
The program suggest that: "One week a month, allow your muscles to rest by doing the workouts several levels below your normal level"
People that are on say lvl 5 or higher will post 50+ rounds for D1 if they are using L1 as their rest week.