It is true, but not for the underlying reasons that they all believe. It's not because they are Iranian, it is because the Iranian government takes its own sweet time answering the requests generated by CSIS. This is also true of those in other middle eastern countries as well as African and South American countries. If you read the boards of those waiting for their PR, you will find some stuck in background checks from Russia and Kazakhstan as well.
CSIS and ICC are not looking at your place of birth or your passport and trying to find ways to 'delay' you, however your native country has ways of delaying all of it on your behalf by not answering requests in a timely manner ...
I hope you all get to oath soon.