How scary is the move Mary Reilly?

I had a fanfiction in mind for the musical Jekyll and Hyde and I was asking a few peoples opinions on FanFiction.net. One person read the description of my plan and told me to watch Mary Reilly because the ending may give me some ideas. I watched the trailer when I saw that it was a horror/ thriller movie. The movie looks really good and I would like to watch it but I don't do good with horror movies. Could someone tell me how scary it is? Or compare it to another horror movie you have seen? I few horror movies I have seen are Orphan, Sleepy Hollow, Black Swan, Shutter Island and I want to see Case 39. I am 15 by the way.