I do not remember actually who posted a response from Visa office New delhi but there was a thread in which it was mentioned that even though the medicals and passport were request the security check is still ongoing and VISA will not be stamped unless VO is satisfied that applicant is admissible to Canada
So it means that even after medicals and PPR there are certain checks that may continue and this may justify why some people get passports in 2-3 weeks and why others tale 15 to 16 weeks. The average time though to get the passport back is about 5 to 7 weeks