If it was the same P2-ISM that I flew back in the early 90's it had 300hp FI engines.
Sad news.
I once brought a similar Islander back to Kerema after losing the LH engine in the Hauwabaga circuit area
, just when about to turn base (which would have committed me to land.)
With 25/25 set on the remaining engine I certainly could not climb and indeed could not even maintain 5,300' (circuit height HWB) and had to fly the long way round the ranges back to Kerema. The aircraft was empty except for around 75 to 100 kg of coffee beans in bags (and mein Gott but did that smell beautiful!!
) and about half tanks of fuel.
From memory, I finally found I could hold just under 4,000' at about 95KIAS
.
Mind you, this was 25 years ago.
Edited to add; The Islander I flew in the above mentioned incident was indeed ISM. It was then owned by the Catholic diocese of Kerema,and flown by Simbu Aviation Pilots.