Backups + streaming replication + WAL-E

Hi,

In our company we user Postgres v 9.4, with streaming replication (master +
one replica).
We use WAL-E for backups (WAL files continuously archiving to S3), and use
wal-e backup-push every night.
Unfortunately, I see performance degradation while backup-push running, so
I use "--cluster-read-rate-limit" option.
For now, backup starting at 05:00 and ends at 12:00 (7 hours). And this
time getting bigger and bigger every day. I am not satisfied with this
solution.
We have one replica node. Is there any options to use replica as a source
for backups? Or some other scenarios?
Also, our app running in OpenStack cloud and we can easily do snapshots for
our disks. Maybe we should use this feature to solve very long backup time?

Thank you!

--
Maks