Startup speed very slow >20 sec

Hello everyone,

Installing Collabora Online 6.10 or 6.XX in my Nextcloud 21.03 environment as docker or build CODE I noticed that it will start rather slow.
After loading the Collabora environment within 2 -3 sec it takes up to 20 sec to start with an empty document. The cloud-server runs on a proxmox server with 20 real cores, and 32Gb, that should be more than sufficent, hard dirves are SSDs.
Changing the browser from Chrom to Firefox or Vivaldi did not help in any way and I accessing over a lan.
Because it is so slow it will be hard to integrate this in a working cloud. . Is this a known issue, can it be fixed, did I do something wrong?
Any suggestion is welcome.