Make sure you run the latest version of PHP. Right now that is 7.4 Most hosting providers give you the option to set the version via DirectAdmin or cPanel.
Make sure the PHP extensions
opcache are enabled. With most hosting providers this can be done via DirectAdmin or cPanel.
WP Super Cache
The WP Super Cache plugin turns your website files into static files, so your pages are not delivered from time consuming WordPress scripts, but simply from these static files. This ensures a speed gain since the PHP scripts do not have to be run every time.
Don’t cache dynamic pages! For Fast Events you have to make an exception for every order-page, thank-you-page and the error-page. Add them in the
Advanced tab of the WP Super Cache settings.
The Autoptimize plugin aggregates, minifies and caches scripts and styles, injects CSS in the page head by default but can also inline critical CSS and defer the aggregated full CSS, moves and defers scripts to the footer and minifies HTML. It may boost performance of your site, but make sure you test it. Certainly if you use it in combination with a caching plugin and a CDN.
There is a kind of hidden feature in this plugin that lets you pre-compress the aggregated js and css-files. A real time-saver, instead of compressing these files for every request, it serves the pre-compressed files straight from the cache. Include the following snippet in the Snippets-plugin to enable this feature.
Consider using a CDN. There are many available, but Cloudflare has a free plan. This can give your site really a boost. It requires a fair amount of knowledge to configure this, but there are also hosting providers such as Vimexx that offer this as a standard option in some packages.
Not every hosting provider is offering Redis. But some do and if you have a VPS you can configure it yourself. Install the Redis Object Cache plugin and it will cache objects in memory rather then getting information from the database every time.
Use a Theme optimized for speed
Consider using the GeneratePress theme. At the moment it’s the fastest theme you can get in terms of size and speed. The premium version offers you a ton of features and good support, and is definitely worth the money.
Keep your database as small as possible. If you have finished an event, remove it’s content before you start a new one. Before you do, you can of course export all the orders and tickets for archiving purposes or data analysis.