Considerable slowdown with many lights

I have 7 lights in my scene, and the FPS is considerably lower than I had expected (~15 fps). Only one of the lights is set to cast shadows. If I turn all shadow-casting off, nothing special happens to the fps.

I remember something about using these kind of software lights from when I was into OpenGL programming a few years ago, and that was that if you have more than 3 lights at any given time you'll start to see slowdowns because graphics cards are not keen on software lighting.

Is this something that others here have observed, or am I simply imagining things?

I don't know the answer to your question but this is an Ogre not a Mogre question. It will get answered faster in my forum.

Many lights at the same time degrade the performance.

There is some techniques for simulating light, how light maps.

Try light maps search in the main forum.
Light/shadow maps are precalculated lights for static objects in the scene.