Mail "check for new mail" vs PowerNap

Trying to improve my SpamSieve performance and wondering if I need to run Mail on my iMac file server as well as my daily driver MBP to get best performance.

The MBP obviously spends most of it’s time asleep…PowerNap will wake for checking mail hourly. If I set a 15 minute interval in Mail preferences…does anybody know if that overrides the PowerNap hour and actually checks every 15 minutes?

If it’s only every hour I might have to setup SpamSieve on the fileserver as well as the laptop.