You should try to find out whether the issue has to do with the amount of geometry or with the amount of pixels being drawn.
You can easily do this by resizing the window to be half the size. If rendering the object reduces to only a quarter of the time, then you know it’s got to do with the amount of pixels that are being rendered of the object, not with the amount of geometry. This could be due to excessive overdraw, ie. if you have lots of transparent cards making up the individual leaves that are being drawn over each other. If that is the case, instancing won’t help a bit.