Can you share some details about the size of your repos, in particular the number of Lines of Code for each Languages (you can find this info in SQ itself), the number of files and the total time to scan them?
(don’t forget to mention the version of SonarQube you are using also).
We are working to improve the scan time of Pull Requests so that only the changed files in PR are analyzed instead of analyzing all the files (and report issues only on changed files). This is not yet available but hopefully should come in 2022. This will be a feature of SonarQube Developer Edition.