Slow loading with slider

Hi there, i´m using the Tempera Theme with the integrated slider. The main issue what I have is, that the page first load is very slow till the first picture is available. So my question, what can I do that the pageload gets quicker. The picturesize is 1920 x 600 Pixel, I also compressed the pictures. But it stays slow. What is the best size to get better performance to the startpage.

Regards Andre

Website: insane-on-2-wheels.com