15% are Lutheran? Funny that my friends in Kazakhstan didn't notice this. Maybe they are secret believers. I have to say, I doubt this. And it is true that perhaps one third is ethnically Russian, but that does not make them meaningfully Orthodox or Christian.
No it's because Stalin moved the Volga Germans into Khazakstan during 1941. A lot of them have left, though, for Germany or other countries. There is also a Lutherin presense in Georgia, a former colony under the Tsars.