How long should it take to get through customs/immigration at CDG?
Depends on time of day. Don't recall it being anything outrageous. 10-20 minutes through immigration, Customs is just a matter of walking through the door marked "nothing to declare" with your luggage. If you have checked luggage, that is liable to be your longest wait.
I landed at CDG at 1:00pm on a July day with only carry-on luggage and it took about 20mins.
The last time I went through Passport Control at CDG, December 2012, it took more than an hour. My step-daughter travels with her EU passport and she went through the EU line in about 5 minutes... So don't think that 15 or 20 minutes is what you will always encounter. On another trip, the CDG Immigration agents were "working to rule" so we were in line for a couple of hellish hours.