T.S.
I wouldn't worry about it. It's not so complicated that you can't follow along for the most part.
My 20 year old son MADE me go see The Hobbit with him last December. I am so NOT a fantasy fan, never read Lord of the Rings (which both my husband and son adore) but I was happy to go with him and endure it simply because he wanted me there (and he's still trying to convert me, after all these years LOL!)
Just go and enjoy. I'm sure you'll be entertained enough not to fall asleep. Have a big coffee beforehand if that helps!