Mechanical hard disk? Sounds about right!
I tend to use a symbolic link to make the WIM folder on a RAM disk which speeds it up a lot. The tool that does the patching, DISM, is absolutely brutal on the random read / write operations. Spindle drives hate it!
RTMF (aka watch the video)
1 Image will only do Home, Home Premium, Pro, or Ultimate. They are actually separate images on the disk, so if you want them all patching, it takes 4 times as long (the all_images one).
If you know you're just going to install "Professional" for example, then you can just patch that one (it asks when you run that batch file). If you want the ISO for your toolkit, then you definitely want all images patching.
It's a pain it takes so long....I always knew that was going to be the case, but it's why I made it 'click and forget' in its operation. Most tools out there don't come close to the ease of this.