Reading the script altogether

We're doing our first drama rehearsal altogether, and read the whole script altogether, according to our own characters. Our group members are limited, which only 5 of us. So each of us must play for at least 2 or 3 characters for the play. For myself, I'm playing the characters of the nurse, lady capulet, and the prince. Our first play rehearsal did not work very smooth, with the total timed play of 17 minutes, since we have not read the whole script appropriately. In order to reduce the time, into 15 minutes at least, we need a whole lot of another drama practice, so that the drama would have work better. I am trying to practice my characters' lines of the nurse, prince, and the lady capulet, so that I would have speak more fluently for the real play. While for the narrator part, I wouldn't need to memorize the lines, since I can just read the lines from the paper.