flying into PEK from IAD travelling to hong kong with Air China. Is 2h 15 mn sufficient time?

Hi we have booked a flight with Air China from IAD to Hkg. The flight stops in Beijing (PEK) both times while flying into HKG and out. Layover time during flight in to HKG is 2 hr and flying out of hkg to IAD is 1 h 45 m? Is this sufficient time? Also do we have to do the immigration once again since our tickets say that while IAD to PEK is Airchina, PEK to HKG is operated by Cathay Dragon?

Please help