On sites with hundreds of thousands or millions of members, the Search Members page in the Admin can take a long time to load. One reason this happens is due to a query that checks whether or not there are members that need to be geocoded.
In order to speed up this process, search for the Advanced Setting:
Exact MySQL Queries
System Variable: big_database
When this setting is on the system will not perform the Geocode check and load the Search Members page faster.