"background idle" syncing of filesystems

Hello, I recently upgraded RAM on my Desktop computer (running openSUSE Leap 15.4) to 512GiB ECC DDR5. It's a great speed up, as I do a lot of disk I/O (home filesystem). But if it comes to syncing filesystes, it takes up to twenty minutes to sync them. Hence shutdown/reboot takes ages. (Hardware is a SAS Hardware RAID 1 (megaraid_sas with 2 2TB SAS HDDs)). is it possible to do a regular sync of the filesystem in idle I/O class, e.g. a crontab "ionice -c 3 sync", or would it cause performance issues or some sort of locks? I do not want to loose the speedup by async mounts and buffer/caching. But also worried about possible data loss, e.g. on AC fail. Thank you, regards Paul