Default [Q] [ROM] Increase Screen Lock time (not display off time)

I'm looking for a way to increase the automatic screen lock time for the Tab 2 (sch-i705). Does anyone know where I can find this setting in the system.img?

I'm happy with the display turning off automatically after a minute or so, but I want the device to lock after ~15 minutes after the display turns off.

Couldn't find anyone adjusting this setting on any ROM in my searches.