I can't believe some people are saying "well maybe it's just a temporary solution" as if that is any defence. 15 Hours alone is shocking for an adult dog, let alone two young pups who are probably nervous as it is. Not to mention, dogs hate doing the toilet where they sleep and puppies need to urinate every couple of hours when young and this will have greatly distressed them.
I'd phone the RSPCA again and report that it's now 15hours unattended and the animals are clearly in distress and ask how soon they will be attending to speak to the owner.
And anticonscience, considering phoning the police is not ridiculous. The RSPCA inspectorate is not a law enforcement body, doesn't have special legal powers, and have no right to enter/force you to answer their questions. What they can do is issue criminal proceedings against offenders, done by way of private prosection. Therefore in this circumstance where it appears clear that the Animal Welfare act has been breached, notifying the police is entirely appropriate.
"The Parliamentary Under-Secretary of State, Department for Environment, Food and Rural Affairs (Lord Davies of Oldham): Charities have no power under the Animal Welfare Act 2006 to seize pet animals. The power of seizure can be exercised only by a police officer, an officer of a local authority or Animal Health"