The changelist also mentions that the update fixes another bug that caused the app to crash. Install the update and you will be able to send and receive PDF files using WhatsApp; version 2.12.15 also has an improved design for browsing photos and videos. And the update allows users to zoom in on a video playing on the messaging app.
After installing the update, you will be able to share photos and videos that come from other apps installed on your phone such as Google Drive, Dropbox or Microsoft OneDrive. Simply open "Photo/Video Library" and tap "Choose from another app...". Lastly, the update allows iOS users with WhatsApp to choose from "a variety of solid colors" for their chat background.
If you have WhatsApp installed on your iPhone, you really should head over to the App Store and install the update right away. This way, you will be able to use the messaging app without worrying how much of your free storage it will consume.
source: WhatsApp (iOS|Android) via RedmondPie