The main SongKong window contains some useful performance statistics on the task bar at the bottom of the window.
When SongKong is started the maximum memory it can ever use is specified, this is the second value and SongKong can never use more memory than this regardless of how much memory your computer actually has whereas the first value is how much of that memory SongKong is actually using. Note that SongKong uses a garbage collector to release memory that is no longer required and this is called periodically, if SongKong is nowhere near max memory usage it tries to recover memory less often than it could, and so the current memory usage may be higher than SongKong is actually using.
Under normal circumstances you should need to modify the memory settings, but increasing the memory allocated to SongKong may improve performance. If you encounter a memory problem increasing the memory levels should alleviate the issue.