As susan_cassidy said.
If you want highlights to sync across Kindle devices, you will need to use Amazon's Personal Documents Service.
But they don't accept files that big.
You're stuck.
Do those images need to be that big? Can you try downsizing them, lowering the image quality to something that still looks good on your Kindle
but isn't as large.
You can get some savings by using any of several tools to strip out useless metadata from the images, but probably not 37MB worth...