Postgresql shared_buffer and SHMMAX configuration

Hi,

Recently we upgraded our production server RAM from 7.5GB to 15GB for the
following reasons:
    1. to solve performance issues
    2. the number of concurrent users increased from 150 to 300

Our production server is not a dedicated database server and is being shared
with our other application softwares like:
    1. Tomcat
    2. Apache
    3. Cron based scheduled programs
    4. Also few Java-based thread programs
all running in the same server.

We are trying to configure postgresql parameters with 15GB RAM.

Linux
---------------
Kernal.SHMMAX
    From - 2147483648
    To   - 19818063053

250kB + 8.2kB * shared_buffers + 14.2kB * max_connections
(250kB + 8.2kB * 2359296kB(2304*1024) + 14.2kB * 500) = 19353577.2 * 1024 =
19818063052.8

postgresql.conf
--------------------
shared_buffers
    From - 1536MB
    To - 2304MB

Since we have other application also running we have taken 15% of the RAM
value for shared_buffers.

max_connection
    From - 500
    To - 500

PGPOOL configuration
---------------------
num_init_children
    From - 150
    To - 420
child_max_connections
    From - 20
    To - 30

We have more than 300 Users accessing our server concurrently so we need
around 300 concurrent connections.

My questions are:
1) Is my tuning of PostgreSQL parameters to 15 GB RAM configuration correct?
Experts advice/recommendation on this are highly appreciated.
2) Will the above configuration improve the performance of the database
overall?

Thanks in advance

Regards
Gnanam