WHAT is an IPC?? Do you mean Instrument Rating Renewal??
Speak Strine will ya?!
that “Forecast QNH” is written, opposed to area QNH assuming within the 15 minutes.
??
Neither the (Aerodrome) Forecast QNH or Area QNH have anything to do with the 15 minutes.
If you are using the Area QNH (there's no such thing as an "actual" area QNH) you have to add 50ft to the shaded MDA (DAP) or the Jepp "Forecast Terminal QNH" MDA. AIP ENR 1.5 section 5.3.4 refers. I will not even attempt to find the ref in the useless Jepp Airway Manual.
If you are using an Aerodrome Forecast QNH ie from a TAF, you don't need to add the 50ft. Just use the shaded MDA (DAP) or the "forecast Terminal QNH" (Jepp). AIP ENR 5.3.2 refers.