Do something when light is turned off, but only if it has been on for at least 15 minutes

Configuration
3

Isn’t this a variation of the motion activated lights automation in the Cookbook?

As a starting point…

triggers:
  - trigger: state
    entity_id: light.bathroom_light           # change this
    to: 'on'
    for:
      minutes: 15
  - trigger: state
    entity_id: light.bathroom_light           # change this
    to: 'off'
actions:
  - action: "switch.turn_{{ trigger.to_state.state }}"
    target:
      entity_id: switch.bathroom_fan          # change this

Another option would be to have an input_boolean flag that is turned on when the light has been on for 15 minutes, then use that as a condition in an automation triggered by the light turning off.

Or… Trigger when the light has been on for 15 minutes, then wait for trigger with the light going off.