Reducing pdf layers and file size

Hi, 

I'm trying to create a pdf. It is a 24 page A6 booklet that has alot of different layers and objects but I need to reduce the layers so when it opens up, all the different elements open up separately and it takes a while for it all to show. The same happens when scrolling through the pages. 

The file size isn't too large from what it was, but it could still be smaller and I think if i could "merge" the layers into one layer then the file size would reduce, at the moment it is 6mb. 

I've already tried saving it through different settings on Illustrator, merging layers, rasterizing layers, I've tried "reducing file size" through Adobe Acrobat and that doesn't work. Adobe Acrobat is not actually showing all the layers as Illustrator does. 

The document was made on Illustrator and there are a lot of different vector and raster imagne conent

Any help would be greatly appreciated.