I have winter tyres on my ZS, so not the same size as you but I see the benefits
I have put them on my ZS wheels which is also a not too often seen size and they cost 450 euros including fitting for some Pirelli SnowControl something or others.
Then for summer I'll get some new alloys so I also have 2 sets.
Actually for snow, a thinner tyre is better, because it will cut through the snow better. I think 15 inch is fine for the brakes but im not sure so someone else will need to confirm.
Also a tip would be to stick to the big brand names, such as pirelli, bridgestone, continental, michelin, goodyear, dunlop.
Over here in the ST size 205/45R17, ur looking at 200 euros per tyre for Pirelli Winter SottoZero 2's
Based on that I would say the Vredesteins you showed are about the right price (They are 218 per tyre here)
I would say if you can afford 800+ euros on winter tyres every say 3 years for ur ST wheels then go ahead, but I think you could save a lot of money with a smaller wheel and a more common tyre size