Is it necessary to have so many files? You could combine the files to have fewer entries in the OPF. This would help with your other OPF that's 415K in size.
If you need pagination, you could accomplish that with page-breaks, like this:
<br clear="all" style="page-break-before:always"/>
Or put something in your CSS:
.break {
page-break-before: always;
}
Then use <div class="break"></div> where needed.