As someone who has hosted a few Nextcloud instances for a few years: Nextcloud can be quick if you make it work. If you want to get a good feel for how it can be rent a Hetzner storage box (1TB for below 5 Euros a month).
You sadly can't just install nextcloud on your vanilla server and expect it to perform well.
You sadly can't just install nextcloud on your vanilla server and expect it to perform well.