If your file has a large size and your scenes are apparently empty it means there are other datablocks saved in your file but not in current use in your scenes, or at least your current scene.
Try switching your Outliner to Group view and you will find plenty of group definitions you can insert into your scene, with lots of high poly objects stored in them.
Otherwise if this is not the case, go into the Outliner and change the view context to Datablocks; for Blender 2.8+ versions you can use both or Blender File or Data API display modes. There you can see a list of categories containing different data-types stored inside your file, like images, objects, groups, brushes, etc. This should give a hint at what is taking the most space inside your blend file.
After that you can also have a look at orphaned data. To see this in the Outliner change display mode to Orphan Data and see what data is unused but still saved inside your file. If any is undesirable you can purge it all using the Purge button up top right, or individually by right clicking the item and choosing Delete or Unlink.
To actually delete data, select the (un)desired groups in the Outliner under Group mode, Right Click over the group name (not the icon) and choose Unlink option.
Pre Blender 2.8, you have to save the file, quit Blender and then reopen the file again, for actual data to be gone. Save again and file size should be reduced.
For 2.8+ you can check again the Orphan Data in the Outliner and repeat the steps described above.
For you particular case, only way I figured out how to actually reduce file was to go into the Outliner, after unlinking all groups as described above, switch to Blender File mode, go into the Mesh category and manually select everything and erase it with Right Click > Delete. This reduced file size to about 5Mb
Due to the large amount it is probably easier to just select everything with A and deselect all other categories before erasing