Assuming the system stills works at all and hasn't been destroyed by freezing, it would depend on the design of the radiator system, i.e. size of radiators and how they are piped. A system designed to emit 15kW max (at say 60°C flow) is going to struggle to emit more than about 23kW max (at say 80°C flow)But if we now consider the conditions I outlined above namely: -5C outside and -5 inside — due to leaving the house empty and unheated during a 2 week cold-spell. With this scenario, when I return from holiday, I now wish to heat the house as quickly as possible to reach 20C, and so the boiler can ramp-up to 30kW, and then modulate down to 13kW when 20C is reached?
The 'perceived temperature' of a house depends roughly 50:50 on the air temperature and the temperature of the surfaces. You can get the air temperature up fairly quickly (hours) but warming the fabric of the building can take several days.
I'd recommend that you leave the house with the heating set at 10°C and the stopcocks off.