Ok, right off the bat i see a huge problem, why are you using two disk cache based plugins?
I would recommend you use WP Rocket and disable WP fastest cache, you should never have two caching plugins enabled, unless you have some sort of complimentary caching system with an object cache which you don't.
Also what hosting are you using? There is no such thing as a dedicated VPS. Are you using a dedicated server? Or a VPS like Amazon EC2, Vultr etc? VPS's are not actually dedicated in any sense of the word.
I haven't seen the site yet but i have a feeling that your site would improve by....
- Selectively loading your assets on pages.
- Cleaning your database.
- Checking for query performance issues.
- Removing one of those caching plugins (I guarantee they are causing your TTFB to spike making search engines lower your site rank.)
I have a lot of suggestions, please message me i'd love to take a look at your site.