Mine was projected at 19 months when I filed online - but I finished in about 5 months.
Everyone's experience will vary based on where their ASC is, how busy those processing centers are are, and a bunch of other factors.
Where folks can potentially get stuck are the name and background check. From what I have observed, folks move quickly from the time they receive their NOA up to biometrics - and then the time varies between biometrics and the citizenship interview, and then again between the interview and the oath ceremony.
Of course, life happens too - there may be RFEs, some folks get a form that says while they passed their civics test and English test the application needs further review before approval, some folks reshcedule their biometrics, interview or oath taking.
There are a lot of threads around here on the pros and cons of filing online, suggest you check them out.
For me, it went fast processing-wise----everyone's mileage is going to vary of course...speed mostly depends on the field office handling your case.
You can check my timeline in my signature. Best of luck with your filing!
