Hard to say, you might get lucky. I haven't used the PVG service, but on LHR-CTU earlier this year I took the entire middle block of 4 seats near the back of the A330, so had a great sleep! Flying in Premium Economy on LHR-PEK (on their A350) the PE cabin was very quiet - maybe 8 people in a cabin with 24 seats IIRC.
Conversely, when I was on the B777 LHR-PEK service in Economy, it was quite busy and I had someone next to me all the way.