What causes this warning on Safari? "This webpage is using significant energy. Closing it may improve the responsiveness of your Mac"
This message is caused by Safari watchdog process that monitors the Javascript scripts running on a page. It is there to notify the user when a script is utilizing too many resources. Your page when loaded on my computer raises the CPU utilization to 68 percent. Be weary of loops and custom render code.
Notes for improvement:
Make the rendering code as efficient as possible.
Combine the your internal Javascript files into a single file, instead of 7 files. Major improvement.
When possible(due to licensing and update considerations) include the 9 external scripts into the single file stated above. Minor improvement.
Split the main page into different sections either as separate pages or dynamically loaded using AJAX. Major improvement.
Avoid svg files. SVG files require a lot of computing power to rasterize and display. This is the main cause of the 7 second load times. Convert the files to png at the largest expected display resolution and offer an expanded SVG file if more detail is wanted(by click or delayed mouse over). Major improvement.
The number of images is not the issue. It is the number of SVG images(on load) and the scripts causing the issue.