The heat dissipated by your central heating equals the amount of heat that leaves the house through the insulation at the end of the day.
The amount of heat that leaves through the insulation is proportional to the temperature difference between inside and out so, if you set the thermostat at a given temperature that maintains a certain difference between inside and outside, the more hours in the day you have the heating on, the more it will cost.
Yes, if you let the house go cold overnight the heating will run for a longer time in the morning until the set temperature is reached but this is more than offset by the lower level of heat loss overnight due to the cooler house.
You wouldn't consider a kettle more efficient if it was constantly at boiling point rather than boiled every time you want a cup of tea.. the same principle applies.

I really don't understand the logic behind the 15 minutes an hour, except perhaps that a condensing boiler will be more efficient while the system is relatively cool so preventing "rapid cycling" on the thermostat and giving it a blast every 15 minutes may be beneficial. A modern electronic thermostat will prevent that anyway, however, and 15 minutes in the hour will do naff all when it's really cold outside.
.. of course, if you find a constant lower level of heating more comfortable than a higher setting for parts of the day it may be more efficient, but, IMHO, it's still madness to heat it while everyone is out, for example.
I personally find I cannot sleep with any level of heating on at night.. Unless it's extremely cold outside.