I would call myself an atypically fast reader, but 1.5 to 2 hours doesn't sound too bad for a chapter of Kaplan review. For me, I have to take notes on the most important points or I barely retain anything. Even though I don't usually look much at the notes later, just taking them forces me to actually think about the content instead of just mowing through it being like yeah I understand that.
I've found that doing all the "preview" stuff for a Kaplan lesson in one day is a pretty hefty task, even if you have 8 hours to devote to it so I wouldn't sweat too much. I "started" the class on may 13 and finished my content review (preview chapters, workshops & quizzes, online lessons, and review topical tests) a couple days ago. This took 4 hours for 3 days per week and 6 hours for the other 4 days per week for a total of 12+24 = 36 hours per week. I stopped going to the actual classroom because I found the online lessons to be better than the instructors and I could do an online lesson in about 2 hours without being slowed down by the basic questions asked by many of the students in my class.