Those are interesting and valid questions. I don't know about 2015, but WION had footage of the recent elections in those ethnic Russian regions and it seemed to be an orderly process. If you have found evidence of cheating, please share the link.

One thing I don't get is why Americans assume the voting in other places is less accurate. Here we've got the running jokes about dead people voting in some places. I think there is no reason to assume that voting in, say, India, or Germany, or Japan, is more corrupt.

If there is actual evidence that the voting was rigged, it needs to be presented.