Sony Xperia L device memory is being eaten up
It needn't necessarily be tombstones and thumbnails that takes up your phone's data storage.

Normal app usage (mostly browser cache, etc.) also consumes space over time.

Have a look at

Settings-&gt;App-&gt;All apps


then via menu let them Sort by size to see the biggest storage consumers.

E.g. my phone's biggest consumer is Chrome (123MB data, 280MB cache):

.