Spotlight is designed to place no more than 2% load on your database.
If you want to reduce the server load even further there are a few
techniques you can use.

First and foremost, you can reduce the frequency with which Spotlight
queries the database. By default, Spotlight refreshes itself every 15
seconds for data that is currently being displayed (foreground refresh
rate), and every 60 seconds for data that is to be collected but is not
currently being displayed (background refresh rate).

You can change this via a Spotlight Option. From the View menu, select
Options, Spotlight Console, Data Collection tab, and modify the refresh
rates.

Alternatively, you can change the Overhead Settings by clicking the
Flag icon on the toolbar. If you move the slider to "Lower Impact"
setting, several of the more expensive Spotlight queries will not run;
and also some queries will only be executed when the associated
drilldown is being displayed.