Hi Pramod,
This is pretty hard in explaining what is correct or incorrect here, as we only see the results of your tests, not the tests themselves.
I will assume you are using objectify (by the "@cache" you mention). In any case, I would look up
this doc on objectify, as it points to some caveats about the Global Cache.
In any case, if your question is "how do I use @cache to increase read speed of my application" then it is perhaps better suited to Stack Overflow. I would suggest you post on that forum, making sure you include your code, the code without caching, the code with caching, and the results of your tests. We do monitor Stack Overflow, so if the community doesn't answer you, there is a chance one of the Google Cloud Platform Support team does.
Cheers!