App is kept in memory, content is not

On my GPE S4 (Android 5.0.1), if I change from Firefox or Google Sheets or ezPDFreader to another application for more than 1 or 2 minutes, and come back, the data is loaded again. It is not only bad for my data plan, but is also time consuming. I monitor data usage, it is not just re-rendering. On my Nexus 4 (Android 5.0), applications in the background keep content for an hour or more. It is quite strange, as they have the same amount of memory, 2GB. Is there a setting for this? How can I avoid unnecessary reloads?