Magento page loading taking too much time

As the question seems to be not very magento centric, here is my not very magento centric answer.

OpCode caching and DB optimizations are a good way to accelerate your web applications to some extent. But the benefit will be relatively moderate. To get a real speed boost you should consider using varnish cache. It is open source, easy to configure and easy to integrate with magento thanks to freely available modules for magento.

There is also a good article with a brief overview of how it works: http://www.fabrizio-branca.de/make-your-magento-store-fly-using-varnish.html

Especially consider the chart:

If your business is reliant on your hosting performing well, why are you trying to administrate the server with no experience.

You surely would benefit just by contacting a specialist Magento host and letting them take care of the system administration, whilst you do what you are good at, managing your store.

Looking at your specs, you don't have enough RAM to be trying to run a Magento store. There is a load of similar questions like yours,

https://serverfault.com/a/400748/113375.
https://serverfault.com/questions/430565/magento-hosting-on-a-budget