In addition to 2 Pet. 2.9, in Revelation 6.10, the martyrs ask the same question you are: "How long is long enough?" The answer given there (Rev. 6.11) is that more suffering is still in the offing. Apparently sometimes God even allows evil to happen to accomplish His purposes. "Things will get worse before they get better," God is saying. He says the same thing in Habakkuk 1.5-11. And in Hab. 1.2 and 2.6 the prophet asks the same question: "How long must this go on?"

For one, we know that persecution purifies the church. Secondly, to wait allows more people the opportunity to turn to him. The logic is that when God knows no one else will turn to him no matter what, that is when the end will come—when hearts are so hard and minds are so dark that there is no more hope. Until that time, we must trust the wisdom of God (the point of Job; Hab. 3.16-19).

The people Peter wrote to must have been thinking the same thing. Peter said, "The Lord isn't really being slow about his promise, as some people think. No, he is being patient for your sake. He does not want anyone to be destroyed, but wants everyone to repent." (II Peter 3:9 NLT)

God is waiting for more people to believe His offer of salvation.

How long does God need to leave the world in this state of affairs before he goes ahead with Armageddon? Hasn't 6000+ years been more than enough time to prove, beyond a shadow of doubt, whatever it was He was trying to prove? If He loves us, why does he let us suffer so long? Wouldn't that turn more people against him than towards?