It appears to be random where the eggs appear, because I swear I did not find any of my eggs in the Post Pixie's box.
Yes, I found 16. How that happened was:
I was lurking this forum and saw that a total of 15 had been found. I went and found my fifteen eggs. Then I saw somebody posting that they'd found one of their eggs in a place I had not looked before (the pedigree page), and lo and behold, when I looked there there was another (sixteenth) egg.
When I picked it up it specifically said something like "looks like it's the last one".
Good luck hunting, everybody! 