As ValJEANVAL says about the number 14, separately, they are nothing at all. The fourteen first are a set of fragments and the number 15 is a small hint for the final composition.
I quite enjoyed this. Though part eight is EVIL INCARNATE. Like... seriously. Putting the pieces together was neat though 8D But I couldn't quite figure out how the top three pieces attached.
Thanks Chibinecco and Hydrazoid, your patience deserves a reward. Part 2, like 1 and 3, should be rotated, but in the opposite direction (II => :) The horrible piece 8 should also be rotated, but a little more (8 => 8) By last: What piece remains unplaced? Is there really IIV? If you look in the mirror, you will see who already knows what to do.
I'm giving up on solving 8 and 13. I made a nice-looking picture in my paint window by flipping the right side which I had onto the left side which I didn't have. The mirror saves the day and my sanity!