How do I choose which book outline to write first when I have 15?

I have 15 book outlines and I can't decide which one to work on first, I used to have 600 book ideas but I narrowed it down to my best 15 book outlines. I hope I don't waste too much time debating between ideas and trying to determine which one to finish first.

How do I choose which book outline to write first when I have 15?
Post Opinion