SQL Server Memory allocation and max server memory setting
Your configuration is fine. 24GB total RAM, 19GB for SQL Server leaving 5GB for the OS.

SQL Server is memory hungry and will consume all the 19GB available, that is perfectly normal.

You could lower the max server memory from 19GB. I wouldn't do that however, if you were experiencing memory pressure with 12GB of memory.

The question would be what other roles is that server performing that would use the memory you would potentially deallocate from SQL Server? Can those roles (maybe SSIS, SSRS, SSAS etc) be moved to an alternative server?