>> so far it has taken nearly 18 hours to download witcher 3 to 76%. Forza horizon 2 took nearly 23 hours to get to 68%. then it told me i had to update my controllers.
This type of problem/issue is not just limited to the XB1 it is across all consoles and PC's.
Basically it appears your network connection from your XB1 to the servers is slow although how slow is slow is annother issue. From what I can gather The Witcher 3 download is anything from 35GB plus. So assuming that size to download is actually 35GB then if you only got 76% after 18 hours your network download speed is approximately 2.4 MB/s.
Looking at your Forza download which would normally be 39.23GB, so 23 hours to get 68% would work out that your network download is applroximately 3.1 MB/s which is not that far off your download speed for The Whicher 3.
Depending on your network and your Service Provider these download speeds may or may not be what you expected. Where I live which is Sydney Australia I do get similar download speeds although on occasion I have seen 10 MB/s bursts.
Personally I am not into digital downloads unless the files are relatively small mainly due to the limitation on network speed where I live. This would be the case for the majority of internet users although I won't deny that there are some who can get incredible download speeds. I am well aware that some will say that you only need to do this once however you really should consider the possibilty that that if you really need to reinstall then you are back to a long wait. Still this a topic that has been done to death.