A number of people have complained about this since watch OS2 came out. Personally it wasn't that bad for me an d I updated on the day OS2 launched. It took me 20 minutes to download and around 45 minutes to install. It definitely is slower then it should be in my opinion but it shouldn't really take as long as it has for you. That seems excessive.
By the way there is already a thread on this here ...
Same here. Took forever to update. But I have to say that my ISP had some issues at that time, especially with anything that is connected Apple servers (iPhones, iPads, Apple TV, Watch)