Thank you for reaching out and sorry for the late reply.
You are correct about the sonar.exclusions, it will only exclude files for the analysis but we still need to search in the excluded files for coverage reports.
I am trying to figure out if the slowness is only linked to the coverage search or also the whole scanner itself.
Would you be able to provide the full debug log of the scanner, as well as the JDK version you are using? This would help us pinpoint the issue.
Also, do you have a rough idea of the number of files in your data folder?
We have created a ticket that may help with the lookup of the coverage files. Still, it would be good to have more information to see if the scope of the issue is broader than the one covered in the ticket.