Recording smooth animations is tricky. I've started making videos for Don's products on our market and it can be tricky to rotate the camera around avatars. It's not lag that makes it difficult for me, it's the poor camera controls. They don't provide a nice way to do a smooth rotation.
Is this what you're talking about or is IMVU really laggy for you like freezing? If it's the latter I would first check to see if IMVU lags without the recording software running. If it does then I would check what render mode you have the client set to and enable the FPS counter in the settings to see if it fluctuates. It should stay at a constant 30. Changing render modes could improve performance depending on your laptop's specs.
If IMVU doesn't lag when the recording software is closed then I would run some tests to see if recording other things other than IMVU is also laggy. If it is then I would check my system resource usage with task manager to determine if I am low on anything. If resource usage is high I would close everything I possibly could to free up resources for the recorder and the thing I want to record.
What are your laptop's specs?