Updating the light intensities for ambient and directional lights should be sufficient if you upgrade from r154 to r155. Since your baseline is r149, you probably also have to honor the changes related to color management. Read the following guideline for more details:
BTW: If you want to be on the safe side, upgrade the engine step-by-step (r149 - r150 - r151 and so on) to see when things start to change.