You can run the query against any database as it refers to System Views that are available in any database and they report instance-level data, not data for a specific database.

I like your sense of caution. That's a good disposition to carry around as a DBA, especially as a new DBA, but in thus case you do not have cause to take a backup before running the query as it only selects data.

Before we talk about the ideal memory settings I need to see the results of the query to know if you have AWE enabled.