Website needs to be optimized

I've recently created a blog site and added some content and promotion, but I've noticed that the site is loading very slowly (4-5 seconds on average), using a lightweight theme, plugins and not a few plugins, installing the WP Rocket cache plugin didn't significantly improve performance, and looking at the performance index on mobile it's only 25. I suspect that hosting may be a contributor to the problem, but am not sure how to confirm and fix it. See where I need to look to optimize better.