I installed the kubuntu-desktop package in Ubuntu 12.04 LTS, but the problem is KDE responses very slowly. If I click on an application's icon to run it, it appears after 10 seconds and sometimes does not appear at all. It hangs all the time. The cursor is almost impossible to follow because of the lag.

I have read on the Internet that Unity uses more memory and CPU than KDE. But on my PC Unity runs smoothly and KDE does not.

So what should I do to make KDE as fast, responsive and smooth as Unity?

My specifications are as follows:
RAM: 1.5 GB (DDR2)
Processor: 3 GHz Dual Core
Graphics Card: Intel HD graphics with 256 MB memory.