Installing the latest available patches for legacy software like Acrobat 2015 is critical for several reasons:
This guide provides an overview of the 2015 release, how to find the final updates, and the necessary security considerations. Understanding Adobe Acrobat 2015: Classic vs. Continuous adobe acrobat pro dc 2015 update download
If the automatic updater fails, you can manually download the .msp (Windows) or .dmg (Mac) patch files: Installing the latest available patches for legacy software