how did you get puzzle 15, i'm stuck in that one?

There are hints for all the puzzles in the Virtual Villagers Guide section of the forum.

I need help on puzzle 15 too, I looked at the puzzle guide and I looked up the location, I have level 3 of both construction and building , I just cant find exactly where the chest is, when I drag my master villager over, on the very bottom caption it says "is there something buried there?" But the builder never starts digging, they just walk away, what should I do, please help

Just keep trying. It can take several trys.

Once you have the treasure does it just sit there or are you suppose to do something with it?

It just sits there waiting for people to admire it.

where do ilook after the chest in the game

You can find your hint of that puzzle here.