The file includes are only being parsed when the file is saved because it was implemented like this to more lightweight. The other option would be to always keep parsing the file looking for new includes.
It think it could be implemented to always be parsing the file looking for includes, but I am not sure about the performance impact. I think would be better to abandon this autocomple and try to work with a general autocompleter which can work with all languages.
For now I am not working with it, and I am not sure when I would start looking for this universal autocompleter. There are few project running like https://github.com/SublimeCodeIntel/SublimeCodeIntel