Automation if movement in last x minutes

So I have a motion sensor (I know, awesome, no? ;-)) which seems to be triggering as it should, so that’s already a good thing.
When checking the developer tools it doesn’t seem to have a last triggered attribute (or anything in the likes of it).
But when checking the history of the sensor it does keep track of when it was triggered.

Now, as for my question.

I have an automation (I know, total geek :p) to heat up a room when the temperature is too low.
However I want that to happen only if movement was detected in the room in the last 15 minutes, as to not waste energy. Or even better if movement was detected 3 times or more in the last 15 minutes.

Any idea on how I would need to set this up?

The ID of the sensor is: binary_sensor.bewegingssensor_nal

last-triggered is for automations, not for sensors…there you have last_updated and last_changed
Here you can just use regular automations when state of sensor changed in the last 15 mins.
If you want a counter then you need to add logic e.g. with input_helper keeping track and resetting it

You can use this template which is true if there’s less than 15 minutes since the sensor was changed:
{{ states.binary_sensor.bewegingssensor_nal.last_changed < now()-timedelta(minutes=15) }}

I know, I meant there wasn’t any attribute available indicating when it was last updated/changed.