I485 processing time and security check for Iranians

I have heard and read that for Iranian nationals, they do extended
background checks before I485 gets approved and this might take an
extra year or two. Is this true? Does anyone have info on this?

I am Canadian but I was born in Iran. If the above is true, does it
also apply to me? If so, I am better off
staying on TN or H1 because if I get laid off during the lengthy
process, I'll no longer qualify for TN due to previous intention of
immigrating to the US.