I want to set my radio to a 15m calling frequency, turn the volume up, and passively listen for activity while I do non-ham activities in the shack or elsewhere around the house.
Check your rig's manual. Most modern rigs, even HF rigs, have
scanning features. (Though no one I know uses them).
Program yours to scan up and down the Phone portion
of the 15m band. You can program it to pause for a certain
length of time, or maybe even stop on that freq.