The built in ES scraper is pretty unusable. I use the sselph scraper, and can easily scrape all my systems in a couple hours. That’s with complete sets of ROMs for each.
You can find the sselph scraper in the experimental menu of retropie setup. If you find that doesn’t work properly the manual method is pretty easy as well. Basically you put a copy of the scraper file in the directory for the system you are trying to scrape and set the permissions to 777 using winscp or another FTP client. Then you only have to browse to the system’s directory in the terminal, and run the following command: