I put HD pictures on my website and it takes a lot of time for them to load. I've then tried re-saving them using Photoshop CC as jpeg and choosing 1 in the compression scale (going from 1 to 12). They're much lighter but are still the same size. On my website, I did notice a little improvement in loading speed but it wasn't as drastic as I thought. Would it be best to re-scale the pictures rather than compressing them (since they're never shown on the website in full size, i.e something like 5000 x 3500 pixels). Which is the best solution in order for my pictures to load fast but still maintain a great quality? Thanks!!!
You should nearly always resize the photos before uploading them to a web site. The web designer should be able to tell you what the optimal dimensions are.
Use the option Save for web in Photoshop. The quality level you have to choose depends on the photo. Some can be compressed more without showing compression artifacts. Choose convert to sRGB to avoid problems with colors.
After saving the files use an app like ImageOptim for Mac to delete the exif data and further reduce the file size.