Any tips on making mobile (HTML5) vesion of a course run faster?

Hi, I have developed a game- based storyline quiz that is planned to run on mobiles including phones.

It runs fine on a pc but on an ipad or a phone there are long gaps while it refreshes the screen with the next question. I have made some design choices that may be impacting the speed. So rather than doing loads of testing with various options I wondered if the more experienced members of the community could help or point me to resources where I can get help. Some questions are:

Is it better to load a video into the lesson or point to a video server?

I have chosen to use  'layers' to show the game status rather than use 'states'. Does this slow down the speed?

Any other advice on improving performance on mobile devices would be greatly appreciated.

Ron