shraddhashah:
Generally speaking, the Web Services are far faster than the UI, so your performance problem sounds like it is either the farm itself or maybe the versions of the jQuery librarires you are using.
Given that you have .find("z\\:row, row") in your code - you should be using SPFilterNode - you must be using a jQuery version less than 1.7 and probably an SPServices version less than 0.7.0. Upgrade to the newest versions and let me know if you still see the performance problems.
M.