0.0025pF is too small, you sneeze on it, it's more than 0.0025pF!!!!
When I said HV, I meant over a few hundred volts, if you only have +/-15V, you are safe.
I am improvising here. If you have the big resistor close the the board, layout so that you put a copper strip that is connected to the output of the op-amp. The strip is placed right underneath the big resistor so it become a capacitor to the big resistor. Then you trim the strip until you get the response. Call me crazy, when you are disparate, you need to think way outside the box.............way out!!! Try using a copper tape as the strip, start trimming and see whether you get the result.