The following build had a 15 minute CommitQueueSync stage:
https://uberchromegw.corp.google.com/i/chromeos/builders/beaglebone-paladin/builds/13517
https://luci-logdog.appspot.com/v/?s=chromeos%2Fbb%2Fchromeos%2Fbeaglebone-paladin%2F13517%2F%2B%2Frecipes%2Fsteps%2FCommitQueueSync%2F0%2Fstdout

A big chunk of it was caused by this delay:
05:34:58: INFO: Updating manifest-versions checkout.
05:40:20: WARNING: Could not update manifest-versions checkout.
05:40:20: INFO: Cloning fresh manifest-versions checkout.

Also contributing was b/62300477:
fatal: unable to access 'https://chrome-internal.googlesource.com/chromeos/vendor/rockchip-kernel/': Operation too slow. Less than 1000 bytes/sec transferred the last 300 seconds

There was also a huge chain of 126 kernel patches which took 2-2.5 minutes to cherry-pick.

I have no idea how often this occurs or how often it slows downs builds, but creating a bug to start tracking it.