Some precisions :)
Left Button = Move
Right Button = Zoom
Shift + Left = Rotate
And you must click (or not) for flip "normal" for see the "little green square start root" when you "double click" the button "Grow"
Import object must be "dark grey"
Click again "Grow" for start the process
Click again "Grow" for stop the process (seems you can't have 2 roots in the same time) :wondering

Click "Birth" for create the object
Click "save" for save it

As a leaf = 2 triangles, a brunch segment= 6 triangles it's normal that you obtain big file
Here 800 000 facets
default regulates
35 second create
100 mega (yes) but today machine have 2 gigas memories (Zbrush manage easily 10 000 000 polys)
Render in Anim8Or 25 second (800 * 600 with scanline)
Seems not very long for a an old machine of 3 years old :)

But tell me if you can load "alpha" in the Ivy prog?
me I can't, I must put "Alpha" outside on the resulting object (in Anim8Or for example)