You may consider to check individual image file-size.
If, on average, each image file-size is 200KB , then 40 images will become 8MByte.
To speed up website speed, you may consider to save/optimize the image files to a lower file-size (i.e. lower JPEG quality).
For example, around 100KB for each image, 40 images = 4MByte.
Also, you may consider to employ some CDN (Content Delivery Network, e.g. Amazon EC2, with plugin – W3 super cache or else) to speed up the loading.
Note: Most CDN may require subscription