Yes, but only in a certain aperture range. This is a really complex question to answer, because there doesn't appear to be a "fixed" ISO rating on the 150. It changes based on the overall light level. In low light conditions (conditions where to get proper exposure you need to use f/2) it responds like it's about 200 ISO. In daylight conditions where you'd have to use f/11 to get proper exposure, it responds as if it was 1000 ISO.
Over most of the exposure curve it responds at 500 to 640. But not all. There is no fixed ISO.
