Thats’ pretty much what you get with a 100Mbs connection.
This is definitly too slow and cannot be explained by the 100Mbs networking or the relatively old CPU alone. I use Nextcloud on a home server in a VM on a E3-1240v5 (6th gen Core) with 8GB RAM and SSD storage and when I access it from outside my network, also with a 100Mbs connection, it is significantly faster than yours. The spinning drives certainly play a large part in this. I think SSDs would definitely help a lot here, especially if there are other things running in parallel that generate a lot of I/O (such as torrents). But I also think that there is probably room for improvement in terms of software tuning. A few keywords:
- use / optimize PHP-FPM (FastCGI Process Manager)
- use / optimize meomry cache like Redis, APCu
- Upgrade to Nextcloud 24 and PHP 8.1. Performs noticable better, especially in combination with PHP 8.1.