I don't think you necessarily 'halve' the preparation at all. The essay can ask for a Practice, Person or Ethics or a combination of 2 of these or even all 3. So you have to know all your content. Let's say you did Christianity and Islam. You went in knowing you are going to write about...
I'm sure it'd be fine. As long as it's backing up your point and assisting the overall cohesion of the response. Remember they mark to the syllabus so don't waste too much time going beyond where it's not necessary.
Through extensive research and hacking the Board of Studies secret files, my understanding of the highly complex process is:
Study hard --> Magic calculation process --> High ATAR
Contrary to popular belief, no one has a magic wand that puts 10+ units of content into your head overnight. The way I see it, you have two choices:
1. Continue on your current trajectory ultimately leading to a life filled with dissatisfaction and 'what ifs'.
2. Realise the past cannot be...
Just lock down a quote and technique that you can refer to if they ask for two to write a paragraph with, something perhaps you studied in junior years or analysed as a related text before?
Woah. As a proud Wollongong local I can confirm you elitest Sydneyians are just jealous of our laid back lifestyle*.
*Not srs. It's a shithole. We have a beach. And Jamberoo.