Any reason why? Parked up for the night, well been here since before 11am and this car transporter, which was here before I got here, turns it’s engine on every 3 hours or so for 10-15 minutes.
Luckily I have silicone earplugs so will be fine for sleeping.
Run the aircon to cool the cab?
Batteries on their last legs and knows if he ends up with a cold start it won’t?
Have you asked the driver why he does it?
Juddian:
Batteries on their last legs and knows if he ends up with a cold start it won’t?
Thought frequent starting would not help a cold start. 
jakethesnake:
Juddian:
Batteries on their last legs and knows if he ends up with a cold start it won’t?Thought frequent starting would not help a cold start.
Hence he’s running it for 15 mins at a time, presumably keeping an eye on the voltmeter to see when it drops and stablises.
Maybe running an inverter? Combined with a weaker battery?
jakethesnake:
Juddian:
Batteries on their last legs and knows if he ends up with a cold start it won’t?Thought frequent starting would not help a cold start.
I agree. My battery is not good. It took a whole shift of driving to charge it up. I think 15 mins would be lucky to replace the charge that it took to start it.
I think 15 mins would be lucky to replace the charge that it took to start it
I agree, the op said 10 to 15 so to me that would do more harm than good.
Possibly another reason rather than that. 
My 18 plate had a very annoying low battery warning coupled to a loud audible bleeper. Ten minutes on tickover cancelled it for another few hours.
Finally cured it by unplugging the bleeper!