Most texts that are chosen are indeed chosen because of the heavy content in them.
'Every Man in this Village is a Liar', for example, is rife with imagery filled with conflict, death and the self-inflicted horrors of mankind. It was hard to get through.
Conversely, "Death of a Salesman" nearly brought me to tears as the protagonist suffers with mental illness and suicide.
In a nutshell, many of these texts are chosen by VCAA to provoke these type of responses. And the best way to go about it is to channel those emotions and those feelings towards your opinions of the text.
Ask yourself, why is this moving me?
Why does the text have such an effect on me?
Why am I finding it hard to read through this particular sequence?
These questions will lead to answers that will undoubtedly deepen your understanding of the text.
I always say to my students that one of the most important things in text response is to develop an opinion on the text of study. With an opinion you can express a voice and through that voice, the strength of your writing will by augmented by passion and will therefore have a greater impact on the examiner/teacher reading it. So my advice to you and to any others struggling through their text for the reasons cited in the original post is to use that emotion to hone your stance towards the book into one that is individualised, perceptive and responsive to the themes presented.