Personally, I vary my routine. I actually do the whole 15 mins of reading time. During this time, I really begin to mentally approach how I'm going to do each question. During writing time, I actually try and pace myself over 1 hour and 10 minutes. This gives me 20 minutes to check over the exam, for questions I'm not sure of, or think I need to check over. For me, I find that pacing myself makes me get the question right the first time, and so you don't need to check over the whole thing. As many people have mentioned, its about trying to get it right the first time. I'm saying this from my POV because I've sort of experimented with different ways of doing this, and I've found that pacing myself and going over each question the first time and getting it right the first time really makes it better.
Exam 2 is sort of similar - again, first time, I go through the whole exam and I find that its great because the first time you go over the exam, you actually make sure you try to get it right, minimising your chances of error.
Hope this helped!