Re: Mild understatement
"When the guy turned up to do the necessary, I timed him. Less than 15 minutes from arrival to departure."
There is more to telephone line provision than what you saw out of your window. There's also a reasonable amount of work to do in the exchange.
But, regardless, that fee was set as an average across the whole country. A pre-cabled flat in South London and a farm cottage in the Scottish Highlands both pay the same as part of the Universal Service Obligation.