It's actually a 15 minute "consideration period". Once parked though, that does not matter anymore. What does matter is the "grace period" at the end of the parking session, which is 10 minutes according to Annex B of the PPSCoP.
It is fairly obvious that the charge is wrong as it alleges that the driver "failed to pay for the duration of the stay". As you can evidence a permit that covers the period of parking and that the vehicle left within the permitted time, we have to wonder why they have actually issued this PCN.
I'm actually dealing privately for a PCN issued at the exact same location although in that case, the driver never purchased a permit in the first place.
Is there a requirement to input the vehicle VRM when purchasing a permit? The permit shown does not show any VRM.
There also appears to be an anomaly between the time of the permit purchase and the ANPR entry time. The ANPR shows the vehicle entering the car park at 13:15 yet the permit shows purchase at 13:14, a full minute before the vehicle even entered the car park!
Before we move on to any appeal, can you please provide some answers to the above questions.