If using 1Mb as 30ft (rounded up from 27ft) Then the QNH allowing for the over read of 30ft (630ft Alt) at A should be 1029. In theory, using 1029 and maintaining 8710 ft Altitude should give you the 1500ft clearance.
However! The pressure at B is lower (QNH + 11Mb = 330ft elev = 1016) Therefore, flying from a high pressure area to a lower pressure area, the adage "High to low, beware below" means that the altimeter reading a constant altitude but the aircraft would in fact descend in relation to the MSL. So you would need to fly higher. My suggestion would be the difference between 1029Mb and 1016 Mb ( 13Mb = 390ft) minimum (Altitude of 9100ft).
If you require more accurate, then use 27ft per Mb
Last edited by WASALOADIE; 13th Nov 2018 at 14:51.
Reason: Addition of text