Sensitivity

You have calculated the IRR by making two 'guesses'. That is what we usually do, but making two guesses only ever gives an approximate answer because the relationship is not linear. Here, because it is a perpetuity, you do not need to make two guesses because you can calculate the IRR precisely. It is exactly 150,000/1,000,000 = 15%, and therefore the sensitivity is indeed 25%.

You are welcome :-)