I am pushing almost 550,000 miles driving these TDI's for 15 years and my wifes car it just turning 200,000. We have idled hers plenty of times during those 200,000. I often idle the cars for about an hour in the winter in the morning so I can stay warm while waiting for work to start. The only trouble I have seen in turbo problems is from cars I have purchased with bad turbos or from turbos that sat a long time and caused the vanes to stick. I heard all this stuff about idling is bad for these cars years ago but, too bad, I don't like freezing and I like driving the TDI's. My present car I am driving had just the cartridge installed at 120,000 when I got it. The previous owner blew the turbo. I now have 240,000 on it and that tells me turbo failure is more do to with other factors like wrong oil or driving habits. Don't drive hard from low RPMs, Don't drive hard from cold starts, and then drive them hard once in a while. (and don't drive if something is wrong).
Was your car smoking much when it ran? I had a parts car start running away after it was idling but it was smoking a lot. 15 seconds is too long for a run away and damage happens quick.
Having a run away can be discouraging but rebuild the car and if you do things right they will last for years.