Long processing time for parents/grandparents is not due to how long it takes to actually process the app. It's to do with how many apps CIC was receiving, and what their quota was for visas each year. Quotas are needed for PGP due to the higher demand they will put on healthcare and social services vs typical spousal or foreign worker apps.
CIC approved PGP apps (based on open.canada.ca data) of approx:
2010 - 8,000
2011 - 8,000
2012 - 18,000
2013 - 13,000
2014 - 10,000
Figuring each app has average of 2 people, you can see how many PR visas were actually issued, compared to the 20K+ apps they used to get every year.
Processing times going forward will depend entirely on how many visas they intend to issue going forward vs the cap. After the backlog is cleared, if they dont keep the issuing at approx 20,000 visas per year (based on 10,000 apps cap), then the backlog will just continue to grow again.