Slow in LAN and Slow Gallery


I got NC running in my LAN @home. When I access it over the Internet from at work, I can up- and download with my ISP-Bandwith. So far so good. But when I’m accessing from home, I got something like the ISP-Bandwith as well…With a faster upload.

7MB/s is not very fast within 10Gbe or even 1Gbe. I’m using redis and opcache. But still it is quite slow. The Nextcloud-Database is stored on two SSDs in mirrored ZFS and the Data is stored on 3*1TB ZFS-RAIDZ1. So there shouldn’t be any limitation.
Any idea to improve speed?
And if I want to look at a picture with the gallery app, it is slow as hell. The first ~30 Images are loaded very quickly, the others are very very slow. Around 3 Pics within 20 sec? sometimes it even stops with “Error gallery Exception: Preview generation has failed”

Any ideas?