Companys can charge money like £15 a minute as these numbers are usually from abroad, they will just make it look like a UK number by forwardign you on to the premium rate number. Remeber the dial-up Scams?
As already mentioned above, £15 per min calls are a myth. The max charged for any premium line is £1.50 per min regardless of call origin. Thats on a BT line. Others may vary slightly but not by much !
Simple way to avoid this type of scam though is to not call back numbers that you dont recognise or think look suspicious.