To my knowledge there is no such thing as a "Macbook 13". If you are referring to the size of the screen (13"), then we would need to know the model year of the Macbook, to know which mac you are running.
To my knowledge, there is no preference for Revit 2015 when it comes to Windows 7 or Windows 8.1 - although generally speaking Windows 7 is known to have better performance than Windows 8.1 - which might in turn also impact Revit.
And from one mac user to another, let me just tell you that running Revit on a mac is generally just not an optimal solution. Even though you might get it to work (which i did as well), you will experience weird issues which boils down to the hardware / software on a mac just not being optimized for running Windows. Graphics drivers are often released with an immense delay for Bootcamp too, which means that even known issues might exist on your mac for months (or years) even after they are fixed.
Good news is that being a Revit compatible Windows PC is not that big of an investment and is quickly "made back" in terms of just having compatible hardware/software that don't cost working hours.
