3,2 M for 200 pages isn't normal...
I think you must "validate" your epub or installing sigil as suggested or using standalone tools like this:
http://validator.idpf.org/
thas is the "official" validator of idpf ( but has some issues ) and this:
https://code.google.com/p/epubcheck/
I prefer to use epubchecker that is the program embedded in sigil...
As you have validate your epub, you'll be able to see the cause of.
HP