dry saturated steam at 2 mpa is throttled isentropically to 150 kpa how do i interpolate to find the superheated Temperature?

Did you mean to say isenthapically and not isentropically? The way I would this is go to a Mollier Chart and while staying along the saturation line (where the quality is 100%) look for the 2 mpa curve. The saturation line and 2mpa curve should be intersecting. Now, find the enthalpy lines, these lines will be running perfectly horizontal across the chart. When you find the intersection of the enthalpy line, staturation and 2mpa, move horizontally until you teach .15 mpa. Note: You may not see the exact number, you’ll have to guess where .15 is.also, Notice that you will no longer be on the saturation line this is OK. When you get there look at the temperature lines And make your best guess of what temperature you landed on. There you go, good luck