Naive Bayes too slow

[snippsat]

EDIT: What could be causing this to happen?

You have downloaded all  NLTK data?

>>> import nltk
>>> nltk.download()

A new window should open, showing the NLTK Downloader.
Click on the File menu and select Change Download Directory.
For central installation, set this to C:\nltk_data (Windows),
/usr/local/share/nltk_data (Mac), or /usr/share/nltk_data (Unix).
Next, select the packages or collections you want to download.