Help: Slow Loading/performance Of Site!

We are running 4.12.2 SP2 for one of my clients. We are using UniTheme2 on one storefront and the other I customized the Responsive theme. When I run GTMetrix on UnitTheme the score is an F and I am not sure why. I have reached out to the developer but gotten no response back. We are going to be having a huge sale on the site on Friday and need this figured out before then. Any help from anyone here would be appreciated. I know the issue is with the theme because if I switch over to one of the Responsive themes and run GTMetix the score is better.

The first result is after installing and setting up UniTheme.

The second is switching over to the Responsive Greeny theme

The third is back to UniTheme but with CDN turned on.

website is

I just tried 4 categories and 10 products and after caching didnt seem slow enough to put me off

Yes it could be "snappier" TTFB maybe, but oberall not baaaad.

I know you need to see improvements from an F, but it isnt as bad as first thought on usability