Fifteen months is early even for 100% picture books. It's far too early for understanding a storyline - it's too early for the level of imagination capable of understanding that there could be such a thing as a story.
Most fifteen month olds aren't interested in books except as a very short and quick interaction with daddy/mommy. They probably aren't capable of saying words on the page yet - that's possible, but most do that closer to 18-20 months. My eighteen month old just started going through his book phase, and my older son did the same at that age. But even then, it takes months to learn to read the book in order and not just flip around.
They haven't even really learned to identify pictures on the page with real objects yet, after all. It's not much before fifteen months that they learn that the baby in the mirror is themselves, after all; how should one expect them to learn a picture of a car is a real car? Hence the lack of interest in even picture books - they're just not 'real' to them until they hit that stage of development, usually around 18 months.
At fifteen months I'd be happy with just getting comfortable with sitting on my lap and holding a book, and anything beyond that is a bonus. It sounds like you're really focusing on education, which is good, but fifteen months isn't the time for this sort of education. Social interactions and gross motor skills are mostly what's needed at this point; she will pick up language just from your talking to her.
Finally, I recommend you pay attention to your child's wants and tendencies more. Rather than having some idea and asking why she won't do something, see what she does like and does do, and do that. Responsive parenting is key, especially in the first few years; when I stopped pushing an agenda with my older son and started rolling with what he enjoyed, my life got a lot easier, and it's worked very well with my younger child. I'm still making sure he has lots of opportunities to learn - but I'm going to the science and industry museum instead of the aquarium, because that's what he enjoys.