Aw, if I could just totally revamp the slider for you, it would solve all problems, right? That’s actually not what’s happening, unforutnately. Flexslider (the plugin that sets up the slider) fades in only after the entire browser window has finished loading.
So, in other words, if you see your slider takes 12 seconds to load, it doesn’t mean the slider took 12 seconds to pull your three images of your slider, it means your entire site took 12 seconds to load at that moment for whatever reason.
Common causes for inconstant loading times are pulling data from external sources like YouTube, Vimeo, etc or using an inexpensive shared, web hosting account in which you’re sharing server resources with many other customers getting who knows what kind of traffic or using whatever resources at any moment.
Additionally you could look into a caching plugin like W3 Total Cache possibly paired with a CDN service like Amazon S3.