If it’s at 5-15ms of downtime already, you’re in the space where the “zero” downtime FS might actually cause more downtime. In addition to pauses while the snapshot is taken, you’d need to carefully measure things like performance degradation while the snapshot exists (incurring COW costs) and while it’s being GCed in the background.

Also, the last time I checked the Linux scheduling quanta was about 10ms, so it’s not clear backups are going to even be the maximum duration downtime while the system is healthy.