See this page for some more insight in memory usage of a Mendix app:
The memory will be cleared by the garbage collector when it is no longer being referenced (used).
When the memory keeps increasing up to the limit this is a sign of something unhealthy going on in your app. Some processing that creates a lot of entries or retrieves them and is not ending.
See this page for some best practices on performance:
This is probably nothing to worry about. Because you have so much memory available the garbage collector has not been triggered yet. However, if you see that the garbage collector does get triggered in the future (usually when memory usage is ~90%) but fails to release enough memory then you should investigate.