When i try to start 1.15.2 Server this appered!

https://pastebin.com/iVLueLuf

Where did you download the immersive portals mod that is on your server?

Nevermind, I found it.
There is already a newer version of the mod, try that one. If it still doesn't work report it to the immersive portals issue tracker, as it's an issue with their mod.

Yea as sscards said, this is a problem with immersive portals. If you read line 15, you can see it's crashing on their mixins.