It was unlikely that you'd ever attempt it, but this destruction video makes it crystal clear that it's a very bad idea to boil your iPhone 6S in crayons.
Serial destroyer of iPhones, TechRax, melted down a batch of candles, put an iPhone 6S in the melted wax, and then whacked up the heat. The iPhone 6S gets completely covered in wax, which is probably enough to ruin it, but then it gets things get a little more extreme. Once the screen popped off, the melted and boiling wax was able to hit the phone's innards, completely destroying the handset.
It takes a while for the video to get going; he spends time talking about buying crayons and how crayons look while melting. But if you skip ahead to the two minute mark, you'll see the last fleeting seconds of the iPhone 6S before it gets dunked.
So, if you were at all tempted to boil your iPhone 6S in wax, we'd advise against it. Instead, leave this guy take all the risks; he's the one getting paid for it!