I freed up about 80 GB of storage before the update. The Mac Book has 16 GB of RAM and the internet connection was stable (the update downloaded in proper time given my network conditions). I left it to the update only (Xcode was obviously closed during the period). I am somewhat expecting performance issues with such an old machine, even if the update took 6 hours, I would just shrug it off to the hardware being old. But for it to take nearly a whole day is another ball park entirely.