I thought you were only allowed to write on the question paper (i.e. underline and highlight), not on draft paper or in the answer book?
You are definitely not allowed to write in your answer book. Notes on the draft paper, or on the question paper, are fine. The instructions on the front of each paper where reading time is permitted are quite clear on this (I think!) - and the instructions are usually repeated by the invigilator at the start of the exam.
I'd say use the time as it says: Read but also digest. What do you have to answer - is there more than one part. If so decide how to break it up What is the scenario: formal or informal. Is there any number crunching involved? If so get that out of the way but remember not to have complex maths in the answer. How can you tone it down. If it's graphs - whats the best form? Do this thoroughly and I suspect your 15 mins is up and you can start from a very well informed position, be able to write in a structured & logical manner -- and any other buzz words you see in exam reports! OUTCOME : Pass (or at least hopefully a better chance on an exam with notoriously high fail rate!).