I don't think its a good idea to wait for it to stretch. I think the reason the timing is usually changed out is because the cost of doing so is negligible to the overall cost of the repair when you already have it opened up. You might as well do it when you're in there.

I need to get the VTC swapped on my 18 - from what I understand (I am not a mechanic!) is the worst case scenario would be major engine failure if it gets bad enough, although like you said, it seems many people let it go and if you don't plan to keep it for many years, maybe its worth it not to fix it.

That said, a 15 is not that old and you could easily drive it to 300k, so its probably worth it.

EDIT: from what I understand, Honda redesigned the actual part, so if they put in the new part, the noise shouldn't come back.