So what happens in the 15 minutes you are waiting well her are some options:
That person who handed in about 20 items thirty minutes ago is due back in 5 minutes and all their stuff needs checked.
All the people that have handed in prescriptions and are not waiting in the store but are coming back and they did hand their prescriptions in before you so their medicine needs to be made up before yours.
A doctor has written a prescription that might harm an ill six month old baby and the pharmacist has decided that getting the baby's medication sorted out is a priority.
A doctor is writing an emergency prescription for a terminally ill patient for pain relief and wants to know what the pharmacy has available so he can write a prescription that can be dispensed without the relatives running around all the local pharmacies.
The dispenser is stuck on the phone chasing up stock that should have been delivered but the wholesaler is out of but just happens to have a different make of the same medicine is stock but the wonderful computerised ordering system cannot make the logically jump to send in the other brand.
The enitre computer system has just crashed for the fourth time that day and is getting restarted.
The pharmacist is having to do a minor ailment prescription for someone who has been sent their by their doctor who is trying to save on his prescribing budget and therefore wastes patient and pharmacy time.
And so the list goes on....
If you are lucky enough to get in a pharmacy with nobody in front of you then you should only wait 3 minutes per item.
If you are not happy with the service you are getting at Boots go elsewhere, LLoyds, Rowlands, Co-Op, etc would all be happy to take your prescription.