I'm more familiar withe the LandCruisers and Sequoia, but I don't think you need to change the lower control arms...it wouldn't change anything. The rear tires need to be centered in the wheel well. You can extend the upper control arms if you were getting vibration...and this would tilt the third member back to help eliminate the binding of the drive shaft. I believe this would only be necessary if you were lifted over 3" in the rear. You would probably need to buy a kit to weld into the existing upper control arms...if that were the case. However, if you were over 3" of rear lift, you would probably also need to look at a adjustable panhard bar or a lowering bracket to center the axle in between the frame rails.
Long story short, I don't think you need to mess with anything if you are only doing a 1.5" rear lift. What springs did you buy?