Optimizing Images-that can be the textures of whatever is in your scene, the larger the texture map, the long it takes to optimize if I'm right.

Which I can be wrong, and has been proven! :)

I've gotten this a few times-usually I set up a piece to render, start it and leave.  I noticed, too, when I use dynamic clothing or fabrics in DS3 Advanced, it does take FOREVER to optimize and then to render.   I've tried a few times, and honestly haven't used them since.  For me, it's not worth the time in the rendering process when I have other options of props and morphs to get what I want and paint over for the rest.

I hope someone can help you more than I have-I really don't have an answer, but have run into the same thing myself.