It's been noted that Iray is getting more memory hungry in the latest beta. That, coupled with the tendency of PAs to include 4K maps (a good thing normally), even minor scene elements can consume significant texture memory. With this script, each texture of the selected scene element is reduced by half in each dimension (one-fourth resolution). The new textures are saved into the Studio temporary directory by default, so they'll disappear when the application exits. That means you should save your scene before running the script, not after. If, however, you press CONTROL (COMMAND on OS X) while running the script, the newly scaled images will be saved along side the original textures with the resolution appended to the basename (i.e. xxxx_2048x2048.jpg). Just place the script in one of your content folders. Enjoy.
Edit: added icon
Edit: added Connect compatibility
Edit: Fixed for props / primitives