Takes for fucking ever. I worked with my girlfriend -> fiancee -> wife through her transition between student visa, H1B, green card, citizenship. The whole process took about 7 years.
My wife is here for 15 years now and I am 10. It will be 3 more years before we can apply for citizenship. Combined, the two of us will need over 30 years to become citizens. We already pay 6 figures in federal and state taxes.