Responsive space travel site with in-page tabs using JSON

I'm using json file to fetch data from and swap the relative data on html on click, but the images are appearing a bit after(delayed). What should I do to solve it? Would using preload for images a optimal solution?

The background is getting deformed/resized when data for in-page tabs is changed. I guess a brute force way to solve this would be to set fixed size on background or on main container(?), but what would be a better solution for this?