Choosing right IOPS value in AWS environment

Hi All,

We are running 3 node cluster in AWS environment.
Document count ~ 40M
Currently we are running with provisioned io1 with IOPS between 500 to 1500 based on the load.
From application side we are not expecting this much IO operations per second, but somehow Couchbase is using this much.

Is there any recommended IOPS we should use with Couchbase in production ?
Since EBS io1 is expensive, is there any other way to utilise more IOPS with EBS gp2?