I've read that book and loooooovvvveeeedddd it and I read the sequel, Rebel Angels. I did think of those books when I first discovered LG15. If you have any questions, you can totally ask me.
I would reccomend them to anyone. They are sooo good.
Umm...some similarities I can think of:
1.There is a secret organization called "The Order" that is made up of powerful (like magical) women
2. There is a betrayer (Her name is Sarah but changes her name to Circe, and I'm comparing her to Gemma)
3. Powerful mothers
4. One of parents die (In the book, it was her mother. In LG15, it was her dad)
I can't think of anything else at the moment. Let me think about it.
*edited because I was too enthusiastic and put in too many exclamation points.
