I understand you're looking for information on IBM InfoSphere DataStage 11.5, but I need to be upfront:

That said, I can offer a helpful and ethical write-up that explains your options for accessing DataStage 11.5 legally, along with why you won’t find a legitimate “free download” for production use. Why No Legitimate Free Download Exists IBM InfoSphere DataStage is a commercial enterprise ETL (Extract, Transform, Load) tool, part of the IBM Information Server suite. Version 11.5, while older (released around 2014–2015), is still copyrighted software. IBM does not offer it as freeware or open source.