Yeah, I've noticed it too, havn't done a in depth analysis of it, but I got a feeling uploading a batch eats up a lot of memory and/or process time. I got booted from a cheapy shared server because of it.
Is the memory usage the same when do same thing 2nd time? Maybe some cache getting built somewhere?
There is nothing overwhelming in the code for making galleries. It does cycle through parents and children recursively to build the list to select where to insert the new gallery to. Only thing I can think of is building the gallery list i using the memory (

)
Maybe try the same memory tests when entering a new article directly in joomla. or making a section/category. Not really the same thing, but anyways..
Maybe disable the gallery list in the admin screen and force new galleries to goto "top" and see what memory does. If you don't code, maybe I could make you a branch to mess around with.