I would like to have my laptop be screen saver after 15 secs of inactivity.?

Right-click next to your desktop (not near a component or sidebar) then click "Personalize" and click on "Screen Saver". If an screen saver is selected (if it is no screen saver selected then prime one) change the "Wait: ... minutes" in "Wait 15 minutes" an select the otion "On resume pasword protect".