Do I seriously need to explain that in the Bible, God's commands are relayed by prophets?
If you read the entire chapter, which parts are "God's commands", and which parts are historical documentation of what the people did in response? (Hint: I quoted the prophet's words for a reason)
In case you don't feel like reading that whole thing, as you seem to be partial to simply quoting parts that agree with you
Reading sentences that are meant to be taken together is hard. Adding the previous sentence:
"They entered into a covenant to seek the Lord, the God of their ancestors, with all their heart and soul. All who would not seek the Lord, the God of Israel, were to be put to death, whether small or great, man or woman. "
Understand? This is not a record of them killing "unbelievers", this is a record of them making a covenant (agreement) to do so, after God had commanded them to follow Him. (but there was no command to go on killing/conversion spree)
You'll also note that this promise is followed by peace. ("So the Lord gave them rest on every side. ") This indicates that this was a domestic policy, not a foreign one, seeing as there are plenty of unbelieving countries that the Jews did not attack. Those who lived in the nation of Israel were to follow the God of Israel; but other nations that followed other gods were left alone.
Now, did the Israelites go on a killing spree? It's possible - but it's not necessary, since being put to death is meant as a deterrent. (note the future tense of the covenant)
If I was there, I would be put to death. Non believers, killed right there, just like it says Are you going to challenge what is right there in the bible? Huh, go figure.
If you were a Jew who "would not seek the Lord" living in Judah several thousand years ago, sure. But you'd have fair warning to change your beliefs, as well as strong evidence that it was a good idea.
Consider that the nation had just won a miraculous military victory, and its history was filled with miraculous interventions credited to God. Someone denying the source of those miracles, advocating forsaking God, would be viewed as a threat to the community, seeing as there was also a history of the negative results of that. (invaded by other countries, etc)
This does not, however, remotely translate into Christians being commanded to purge un-believers, or that they're just biding their time. Take the USA - a rather Christian country in its culture: The 1st Amendment clearly protects religious beliefs - and that was codified and approved by Christians!
That you think the Christians are out to get you is along the lines of Blood Libel. Ironic.
PS: I suggest you read about this Jewish guy known as Jesus the Christ if you want to know why Christians have no need/desire to imitate 2 Chronicles 15.
If you want to attack a religion for conversion by the sword, I'd suggest focusing your criticism on the one that is actively killing people every day in this modern era. You do know the one I'm talking about, right?