I shoot RAW images and I thought that Lightroom was really slow, too. Then I realized that when I import images I set the rendering to minimize. When in Library mode and I advance to the next image, it used to take 3-8 seconds of "Loading" before the image was viewable. Then a Lightroom expert suggested that I render 1:1 previews overnight for the folder I am working in. (Library>Previews>Render 1:1 Preview). I did this and now the images load almost instantaneously. And this is on a four year old iMac with only 6GB of RAM. My RAW images are typically between 15-17 MB, so not as big as the OP's images, but my machine is a lot slower. Try this and see if it helps.