help with my cockatiel fastttt!!!!!!!!!!!!!!!!!!!!!?

[Cockatiel]

my cockatiels have been mating ever since i put up the nest box which was on the 4th of march it was a 2 Tuesday's ago. its been 15 days and yet no egg. they mate every single day at least once or twice a day. when will she say eggs? i have heard that there poop gets bigger. will her poop is always the same size (just about). well today i saw her poop a really big poop and a whole bunch threw out the floor. is this a sign of eggs. and if yeah or no when will she lay her eggs im waiting for. also how long does it usually take?