16GB Ram 64-bit server, what configuration to use?

We have a 64-bit clustered Windows 2003 R2 Enterprise
Edition x64 SP 2 running SQL 2005 Standard Edition SP2.
It has 2 Dual-Core AMD Opteron Processor 8212 2GHz.
The SQL Server databases files are on a SAN.

I configured SQL to use a fixed memory of MIN/MAX 12GB
and after one week I see in Task Manager that there is still
2GB of available physical memory.

I'm thinking about changing the setting to MIN 13GB and MAX
14GB to give SQL Server more RAM.

What setting do you think I should set it up for? It is a dedicated
SQL Server box and the only other things that run on this server
is RDP sessions, Anti-Virus, Backup Exec agent. So should I
reserve 2GB of RAM to OS and apps and 14GB for SQL Server
or I could go and use as much as 15GB of RAM?

Also, any experience with SAN fragmentation? There are some
saying SAN does not need to get defragmented. When I ran
windows defragmenter's Analyze button on the disk array where
the MDF file is, I saw it fragmented to 50,000 pieces!

What do you think?

Thank you