I have been instructed to do the 40 day program, but i felt as if only 2 minutes of void meditation are not enough, i have been meditation for 2 weeks now and i always do it for 15 minutes minimum, is it okay to continue doing it for 15 minutes or should i decrease the time to only 2 minutes? And is it okay to breath in energy when doing void meditation or does that will interfere with the mental silence needed to do it properly?

It's ok to do 15 min of void if you have enough will power but as the saying goes here is that you can't run the whole day every day and that's the same for meditation as well in the beginning you have vigour but the vigour will not last if you go maximul every day so the key here is to have common sense, keping it balanced.

When doing the meditation just focus on the here and now don't do other meditations while doing void. Void is for developing a strong concentration ability so focus on that. Keep it balanced.