There is an old trick that I used in Adobe After Effects: Work with low resolution, both for assets and on screen. In AE there is a "Replace" command, where once the composition is done, it is replaced by 4K ones and left at night, while you sleep and rest. It is easy to save a "duf" and reinstall the real files for a better rendering. First pro: Avoid preview times. Second pro: Everything on the screen moves faster. NEVER use the viewport preview in Iray !!. Do a quick render test, and change all the assets. Third pro: When you wake up, you will have a wonderful rendering. Iray is VERY slow to my liking. Better move it to cinema 4D and use V-ray or Arnold. Octane bothers me quite a bit. Render times are lower and of better quality, with little use of denoisers.