Google page insights poor with theme

Hi there,
I am a website designer and have used your theme for many of my client websites.
Recently a few of my clients have ran their website through googles page speed insights and they have come back as poor for mobile and desktop view. Here is a website I am testing right now. https://developers.google.com/speed/pagespeed/insights/?url=http%3A%2F%2Fwww.enclosedtrailers.co.nz&tab=mobile

As far as I can see it is mostly due to how the theme is built?
Do you have any recommendations or updates on your theme that might help improve the google insights at all?

Many thanks
Sami

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