Resize High Resolution Camera Capture to Low Resolution Camera Capture? Say, you captured a high-res image of a scene and a low-res image of the same scene, using a lower-res camera, ensuring that the lower-res camera is using the same technologies, except for the image sensor's resolution. 

If I wanted to drop my higher-res image to the same lower-res image via digitally processing the image, what would be the right approach?

I reckon interpolation or naive downsampling are not the right way-to-go. They seem kinda illogical. I was thinking of using the RAW images and, perhaps, deploying these downsampling therein, and, then, using the pre-processing algorithms for converting the image into the final output. Is there some standard approach available, though?
If you are using a “single-shot” sensor you could simply just not debayer the raw channels.  That would cut your sampling without adding the extra overhead that is already baked into the image acquisition.  A benefit of this approach is that you could probably boost your frame rate at the same time.