Q: Is there a way to globally change polling interval for all maps? i.e. from 30 seconds to 2 minutes
A: The place to change the polling interval is the drop-down list in the lower left corner of each map.
It is a per-map setting.
What you set it to depends on the type of polling you're doing.
If the parameter being monitored is time-sensitive, you may decrease it from the default.
If the response from the monitored device is typically slow (like WMI) or you need to check for changes less often you may wish to lengthen it.