What country are you from? I highly highly recommend confirming that timeline on the forum. there are very few visa offices that actually take that long. as i stated before, if you are getting this "18 months" from the cic webite, it is NOT an average, and that number does not suggest the average time is 18 months. that number suggest 80% of applications are approved WITHIN that time, which means a large majority of applications are approved in less time than 18 months.
Let's first confirm where you are from and then we can see if that is an accurate assumption. my guess is you'd be looking at more of a 8-12 month processing time, possibly less. a large majority of applicants around the world are approved in as much or less than the amount of time it takes to get the OWP for inland.