Website Optimisation (Wordpress)

We have a website, and we are looking to optimize it. Why? Our main market is remote communities where internet connectivity is an issue. Take a look: grey-box.ca , we are a social impact organization, so #code4good ! So our website has to load fast. We use Wordpress, with a Divi template. The site works in 3 languages, and we have about 10k$ of ads per month on it (Google Grant)