Mitchell,
The amount of RAM may well be the limiting factor for the dataset you’re referring to. One possible workaround, if you haven’t already tried it, would be to try processing step two with the 3D Mesh deselected. Once Step 2 is complete, then select “Generate 3D mesh” separately from the Process pull down menu. Related thread below…
https://community.pix4d.com/t/4538-Windows-10-P4D