We often get asked why a site take X amount of seconds to load. Here’s the steps we would recommend in finding the culprit:
Step 1. Disable all caching so that you can get a real picture of performance. Use GTMetrix to take a scan of the site as it is now, and record those results. This will be your baseline, and it’s important to look at the waterfall. It can be anything from external assets, to plugins causing this delay.
Step 2. Disable all plugins, and run a new GTMetrix scan. This will give you a picture of what the maximum performance might could be.
Step 3. Re-enable a plugin, and measure in between enabling plugins. By testing each one, you can see which plugin is adding the most time.
Another great tool to use is the Query Monitor (https://wordpress.org/plugins/query-monitor/). It can give you a breakdown of the load times of each plugin, as well as any errors they are throwing.
Additionally, make sure that you’re using our server caching as well.