I've said this about
ALL IS and got slapped up side the head. Some are slower than others. Some it's the camera processors that slow it down. It depends on the subject and lighting.
But one thing is constant. With IS or VC or whatever they call it,
your focusing will always be slower. It takes time to recognize the situation, then to sense jitters or wiggles or shakes or whatever and then stabilize and take the photo.
It's no good for anything that's moving. That's not what IS does. (yes I understand the setting for panning)
Work around? Yup, I turn off the IS. Rest on something. Carry a monopod. Adjust your exposures or ISO. Don't depend on technology to fix things for us with magic claims and electronics. Without making a guess, I am NOT a fan of IS and I avoid it. But it can be useful sometimes.
Or with stabilization on, take a breath,
breath out, hold, wait, wait, shoot.
But for some people those are unacceptable answers.