make site load up faster

One possibility – I noticed that many (maybe all) of the images in the portfolio slider are 1000 x 667px, but the display is usually something like 260 x 151px.

That means that the browser has to resize every one of them. If possible, pre-size the images to cut down on the amount of data that needs to be loaded and also the time spent resizing.

Maybe divide the portfolio into separate pages and have fewer images in the slider on each page.

You should be able to get an idea of the time savings by setting up a test page with only 4 or 5 images to compare its load time with the portfolio page.