Wrong question.
The right questions to ask are:
– Would I have a lump in my throat whenever I hear the line “Why do I get the feeling you are going to be the death of me?” if I didn’t know that in A New Hope Darth Vader killed Obi-Wan?
– Would watching Anakin and Obi-Wan’s banter be so heart-wrenching if I didn’t know that their relationship fell apart?
– Would Anakin and Padme’s love story be so star-crossed if I didn’t know that they were doomed from the beginning?
– Would I have a bitter smile on my face whenever I see happy Anakin on the screen if I didn’t know that he lost everything, got burned up and stuck in the suit for twenty three years?
If the answer to these questions is “No”, you did the right thing by reading the last page of the book first.