That *is* slow. I assume you've been checked for a thyroid problem?
Rates of metabolism can vary wildly from one person to the next, it seems. My wife literally eats more than I do. When she was younger if she didn't eat enough she just kept losing weight. These days she hasn't had to adjust her eating very much and just runs 10km 3 days a week and her body weight is stable at about 58kg (she's 5'8").
Me, on the other hand..... I have to work on it. I have a thyroid condition whereby my thyroid either isn't functioning or functions very slowly (it was only diagnosed because like a real man I left it until I finally had to go to my GP with a life threatening bout of depression--which I thought was an embarrassing form of mid-life crisis--and she sent me for blood tests....).
In order to maintain what I think is a normal body weight I have to really pay attention to what I eat AND make sure I'm getting enough exercise. My wife can maintain a normal body weight by eating whatever she wants and running 30km a week. I have to count calories, run 50 and lift weights a couple of days a week to achieve the same result. If I don't then my body weight stabilizes at 2 or 3 stone over what I think looks good.
I think the hardest thing for people starting with a deficit of being, say 10 stone overweight, is physically getting to the point of being able to exercise at a high enough intensity (and for long enough) to keep the oven stoked while running on fewer than normal calories. There is a risk of over....er (damn... my English is bad today....) ... er... overexertion or overstressing injuries of the skeleton (did that make any sense?)
Point is, it takes a while before you can exercise comfortably at a high enough aerobic intensity for an hour or so a day and until you can get there, you only have one dial you can turn instead of two.
R..