I’d focus on real performance on your computer, file transfer speed, loading of the interface. These website page tools are a bit special, some optimize their website (many onetime or first time users). So with Nextcloud you benefit a lot from caching. However, if all pages take a few seconds to load, then you have a problem. In this case please use the template with all the information, so we know what you already implemented (like caching -> https://docs.nextcloud.com/server/18/admin_manual/configuration_server/caching_configuration.html).
Regarding the scripts and stuff in the background (chaining requests, cache policies etc.), you can help the developers to optimize stuff https://github.com/nextcloud/server/issues