Assuming this is for Further Maths, what did you think about Mechanics questions in the regular A level? It's all in that same style, long multi-part questions that you could easily get lost in - you have to know your stuff thoroughly. It looks like substantially less work than the statistics - I don't do Statistics so I don't know about the difficulty side of things, but that book is twice as long as the Mechanics book.
Switching would of course be a risk, and would give you less support, so I'd only do it if you were confident in your ability to teach yourself. Also, your teachers might just tell you no.
You mention that you don't understand statistics, but if you're getting good marks in it still then there's no reason to switch. The mechanics won't teach you all that much comparatively, you only learn about three different things.
With practice you would of course be able to excel in Mechanics, as in all subjects.
To summarise, Mechanics seems a shorter topic to learn, but potentially less varied, and you might receive less support. I see no reason to switch unless you are awful at, or absolutely hate, Statistics, but there's nothing from preventing you from doing so, assuming you are a competent mathematician.
Sincerely, a mechanics person