To achieve fast loading pages and normal image transistions, it is best to optimize your images before uploading to your website or adding them into the RapidWeaver 5 Resources.
You can achieve this using your favorite image editor and choose "Save for Web & Devices". Set the DPI value at 72 and use a maximum height/width amount of 1200 pixels. Of course it's best to test your full screen Slideshow on multiple devices and try to lower the maximum amount of the heigth/width when possible. Try to strive for a file size that is below 200kb, keep you image file size small and your website visitors happy.