I think there is a big difference between a beer tasting like one expects a Lager and real Lager. I have done only kits, and never found a kit beer yeast which will do much under 18ðC even then it depends where measured, with a sensor under a sponge or bubble rap so insulated from outside 18ðC is lowest, but where using a stick on temperature stick it measures some where between ambient and fermenter temperature so you may see some activity at lower temperatures.
Even with just kit beers the temperature varies, the Australian beers tend to have a yeast able to work at higher temperatures, British kits start around 19.5ðC and after a few days lift to around 22ðC.
With dried yeasts the temperature required seems to be higher, I bought a Youngs Lager yeast packet, but at 10ðC it was dormant, I am told with liquid yeasts you can go down to 6ðC which is the whole idea of Lager.
So short answer is look at the data sheet for the yeast.
