When you use the Revit rendering tool, the image size or resolution of a rendered image has a predictable effect on render time. Higher values for image size and resolution require more time to generate the rendered image.
If you double the image resolution (for example, from 75 dpi to 150 dpi) without changing other settings, render time can increase by 2 to 4 times. (Depending on the complexity of the image being rendered, the increase in render time can vary from 1.9 to 3.9 times, with an average of 2.7 times the render time of the original 75-dpi image.)
If you double the resolution again (from the original 75 dpi to 150 dpi, then to 300 dpi), each jump in resolution increases render time by 2.7 times. Therefore, if you increase the resolution from 75 dpi to 300 dpi, the render time is typically increased 2.7 x 2.7 times, or about 7.3 times the original 75-dpi render time. If you increase the resolution from 75 dpi to 600 dpi, the render time is typically increased 2.7 x 2.7 x 2.7 times, or about 19.7 times the original 75-dpi render time.
When defining the view area to render, check that the image size is appropriate and reasonable. If you specify a very large image size, the render speed may be very slow.