Firstly, 15km is enough to get the engine warmed up. It isn't as good as a regular blast to fully burn off deposits through the exhaust but it will get rid of condensation, so will help your exhaust system last longer.
I think although you say you understood the answer in your link, I don't think you have. While looking for creamy residue on the oil cap is a good indicator that the oil cas water or something else in it (possibly because of a gasket failure) this is not really relevant to your question.
If we take your question as, "How to maintain a car that drives only short distances in Nordic environment?" then it is relatively simple to answer (in fact I would edit your question to just have this - the remainder of the question doesn't fit with the 1 Question rule here):
While the external cold can be quite extreme in the far north, this is mainly a problem before the car is running, as batteries do not like delivering current when cold - so it can be tricky to start a car in the cold. So you want to install a heavy duty battery.
Ideally, you will also keep the car in a garage, which allows you to keep it a little warmer, and possibly keep it plugged in to a trickle charger through the winter months.
When running, most engines generate sufficient heat that the cold outside isn't a problem. The main exception being long motorway drives - the load on the engine can be very low and the cold air through the radiator can cause a build up of ice that can damage the radiator or other areas - hence the reason for some Arctic trucks to have winter baffles placed over much of the radiator. They also reduce snow blowing in - but from the description of your journeys this probably isn't going to be an issue.
Like I said above, 15km is plenty to get the engine and fluids to a good temperature. But be careful for your first couple of kilometres, as you may find brakes and power steering may not be as effective as once you have fully warmed up the car.