Do Nikon D5100s perform slower with low light without the flash?

I'm still learning about the ins & outs of my camera. I did notice that when I was shooting in low light without the flash, it sounded like the shutter went off significantly slower vs with the flash on.
Normal?
Just want to make sure it's not the camera.

ANY camera will have slower shutter speed with out the flash in low lighting. The longer the shutter stays open the more light it will let in. So yes its normal for the shutter to sound slow because its actually staying open longer.

You should also note that the slower the shutter speed the more likely you are to get a blurry image. Its always best to use a tripod for low light pictures with out a flash.

It's normal.

When the camera is used in any light condition, the time the shutter is open is dependent on the lighting, ISO, and aperture.

If the aperture and ISO remain unchanged, the shutter must be open longer in lower light conditions so that enough light is gathered to properly expose the photo.

By the way, this happens with all cameras; DSLRs, Mirrorless, Point & Shoots. It may be more noticeable with DSLRs due to it's enhanced exposure range.

When a flash is used, the light is no longer considered low-light, and since the sensor receives more light - augmented by the flash - it does not need to be open as long.

Also, for low light situations, Nikon DSLRs at least, have a low-light noise reduction function, that while it cleans up the photo of noise, also requires a finite time to complete. You can reduce the time between photos by turning this function off, but the result may be noisier photos.