Hi, Does anyone know how to drastically reduce epub3 output file size?

I made a series of 16 epub3 picturebooks in Pubcoder with no problems. I've now combined them a into a 624 page omnibus which came out fine, however the epub3 file is too big for the distributer (Draft2Digital) which has a limit of 95Mb and my omnibus comes out as 239 Mb using pixel density 2 amd max jpeg quality , with "reduce pixels to meet iBook Store picture size limits " also ticked.

Tried using min jpeg quality and its still way too big at around 130Mb. I then made each image less than 100kb in Photoshop and replaced all the images but still 117Mb.

Tried using min jpeq quality and Pixel Density at1 which came out at 104Mb.

Removing all sound ( which isn't really what i want to do) still kept it higher than 100Mb. Tried using Calibre which did bring it down to 101 Mb but the picture quality was too poor.

Note: Not too much of a problem as the books can be downloaded separately but would be good to know if there is a solution.