How did the 15 steps of the Seder come to be?  

The Sages designed the Passover Seder as 15 steps to make you enormously successful. Here's the key to unlocking the code.

Passover is a time when any Jew embarks on a personal journey from slavery to freedom.  In order to guide us in our quest, the Sages carefully wrote a book outlining 15 steps to freedom. It's called the Haggadah. The Sages say that Passover occurs on the 15th of Nissan (the Jewish month), to teach us that just as the moon waxes for 15 days, so too our growth must be in 15 gradual steps. Think of these as 15 pieces of the Passover puzzle. Assemble them all and you've got freedom!

Would people add a section? Take one away?  Experiment by doing the whole thing backwards with a Reverse Seder:  https://www.haggadot.com/haggadah/moholo-reverse-seder