Why is my SQL Server consuming so much memory?
Why is my SQL Server consuming so much memory?

You're looking at total process memory, and one particular consumer of memory.  To drill down from total process memory and get a high-level allocation of SQL Server's memory use use sys.dm_os_memory_clerks, eg:
select type,name, (pages_kb + virtual_memory_committed_kb + awe_allocated_kb) / 1024. committed_mb
from sys.dm_os_memory_clerks 
order by committed_mb desc 

or the old-school
dbcc memorystatus
If you see large amounts of process memory (large_page_allocations_kb + locked_page_allocations_kb + virtual_address_space_committed_kb) that can't be accounted for by the memory clerks, see if you have any OleDb drivers for linked server loaded in-process.  They allocate memory outside of the SQL Server memory managers.
The two biggest consumers of memory are the the buffer pool and the lock manager.  Both of these will allocate memory and not release it unless the system is under memory pressure.
MEMORYCLERK_SQLBUFFERPOOL Client-Default        9801MB
OBJECTSTORE_LOCK_MANAGER  Lock Manager : Node 0 6929MB

So there's your answer.  Since it's started SQL Server has at some point grown the buffer pool to 9GB and the lock manager memory to 7GB, which accounts for enough of your 21GB to indicate that you don't really have a problem.
See related: memory used by Locks