Can someone give me an advice why my 2015 12" Mac runs slow? Seek good solutions without buying a new laptop

Unless it is required by your school or employer uninstall Trusteer by following the developer's instructions. AV software is not needed on a Mac and it causes more problems than it solves plus it impacts system performance. And obviously it did not prevent malware from getting on your laptop.

To remove the malware try running MalwareBytes (preferably after uninstalling Trusteer). MalwareBytes is the only AV type product which is known to work on a Mac, but even this app is not usually needed if a user is careful about the websites visited and the email attachments and links clicked.

If you still have issues after doing this, then run another EtreCheck report and post the results again.

Start with getting the adware off your machine. Etrecheck found this:

Adware:

Launchd: /Library/LaunchDaemons/com.GeneralChannelSearchDaemon.plist

Reason: Adware pattern match

Executable: /Library/Application Support/com.GeneralChannelSearchDaemon/GeneralChannelSearch r

Launchd: ~/Library/LaunchAgents/com.GeneralChannelSearch.plist

Reason: Adware pattern match

Executable: ~/Library/Application Support/com.GeneralChannelSearch/GeneralChannelSearch r

Also, in Safari, remove any plugins you have installed, specifically the EPPEX one: https://www.lifewire.com/how-to-view-and-remove-safari-plug-ins-2260895

~Lyssa