basically that size is due to the defauts being loaded independently of them being used or not - for example all animations for all skills and so on.
There are two ways to reduce that size: either by optimizing the resource files, or by removing unused files.
optimizing the files means loading all pictures and audios and saving them with a higher compression rate. This will usually cost quality, but the trick is to keep the quality loss invisible.
That depends on what your target devices are, and is one reason why the company didn't reduce the quality too far in the original files, because quality can't be regained once lost, and some people need the higher quality files.
removing unused resources should only be done near end of development, because you usually don't know what resource you might use in the later game stages. and again it is more difficult to re-add a resources than to keep it until you know you won't ever need it.
A lot of people solve this problem by using project-copies for demos. When you're at a point where you want to distribute a demo of your game, make a copy of the project folder and then remove all unused files from the copy before making the demo from it.
If you then later use one of the removed files there will be no problem because it was kept in the main project.
