Long connecting, wait and receive time for my Apache VPS. Can I reduce them?

Long connecting, wait and receive time for my Apache VPS. Can I reduce them?

I have an Apache VPS. When I'm testing my blog posts page loading times on
Pindom tools, it shows long connecting (192ms), waiting (73ms), and
receiving time (899ms). My some pages loading time goes to 15 seconds. Are
there any way to minimize those times?
Apart from that I run Nginx Admin plug-in on this Apache VPS and its use
cent OS. I have an Intel (R) Xeon (R) CPU E5620 @ 2.40GHz (2 priority and
8+ CPUs) with 1.5 GB RAM. Daily visitors 2,500-3,500 with 4,00-5,500 page
preview. This VPS has only a one wordpress blog.
What are the settings that I should use to optimize these things?
My some Apache configurations.
Timeout 300
TraceEnable Off
ServerSignature Off
ServerTokens ProductOnly
FileETag None
StartServers 5
MinSpareServers 5
MaxSpareServers 10
ServerLimit 256
MaxClients 150
MaxRequestsPerChild 1000
KeepAlive On
KeepAliveTimeout 5
MaxKeepAliveRequests 100
RewriteEngine on
RewriteMap LeechProtect prg:/usr/local/cpanel/bin/leechprotect
RewriteLock /usr/local/apache/logs/rewrite_lock
UserDir public_html
UserDir disabled
Any help really appreciate.
Thanks!