Several things to consider
* Acrobat is absolutely unsuitable for a job of this scale. A few dozen files, sure, a hundred might be ok. 27 million will just cause unprecedented suffering.
* Acrobat is not for server use (if that's the plan)
* If you exclude images from things, there is generally little or (more often) no saving to be made since PDF files are already compressed. Have you actually seen worthwhile results in your tests?