If I repeatedly notice SQL Server reporting a lot of free memory, can I likely remove about that amount of memory from the server without affecting performance? Or, can/should it use more for caching?

For this particular example, the server is running SQL Server 2012 Standard Edition on Windows Server 2012. It has 20 GB of physical memory and hosts over 100 GB of data.
SQL Server is the only application running on the server.

```

SQLServer;Buffer Manager
    Buffer cache hit ratio       99.737 %
    Page life expectancy            874 s
SQLServer:Memory Manager
    Database Cache Memory         6,744 MB
    Free Memory                   5,937 MB
    Optimizer Memory                  5 MB
    SQL Cache Memory                 29 MB
    Target Server Memory         19,015 MB
    Total Server Memory          18,407 MB

```