It's a late morning flight, which are usually not that much delayed (Well, seems some people are more unlucky than others.. today, I've still not have had a single flight within China which was delayed more than one hour..)

1.5hrs in PEK will work unless the incoming aircraft is more than 45min late. (Doors open 45min before departure scheduled SHOULD mean you make it)

You can do a straight connection to the train (T3D to T3E) with such a schedule - assuming normal luck that would mean (with, above 45min before departure scenario) reaching the immigration area around 30-35min before departure. If you show such a tight (but doable) connection you'll be let in front of the immigration queue and also be able to jump the security queue, allowing you to (relatively) comfortable to make your flight. And that's with 45min delay already calculated in. I'd give it 95%+ chance to make the connection. Worst case, CA will have to rebook you (and for a C class pax, they'll usually agree for a reasonable nice hotel if requested)

Flying through PEK, taking the airplane there makes sense. otherwise, For NKG-PEK only, obviously is easier and better for a city to city connection to take the HSR.