If your system really takes 8 seconds to load the next page of the quiz, then there is probably something wrong with your server that could fixed. http://docs.moodle.org/24/en/Performance_FAQ & http://docs.moodle.org/24/en/Performance_recommendations
Adding more button clicks and page loads is not going to solve your problem.
The Ajax-y save and scroll down button your propose would be a lot of work to implement. From where I am sitting, it seems easier for you to tune your server . Also, the thing like that which is worth implementing would be auto-save. See MDL-14963.