The huge difference is that this is the private IP address of his machine (which are basically the same for every device, since it's related to the network you're connected to) and not his public IP address (which shows ISP, country, etc). My private IP address is 192.168.0.20 right now. OP's was 192.168.1.15 when he received the email. Pay attention at the similarity (192.168.x.x).
Also, IP addresses have nothing to do with 2FA.
That is was writen on policy[1]. Take it simple :
Please read the following carefully to understand how and why the Site and the Platform use your IP Address and cookies. If you do not accept or agree to the practices described in this Policy, you must exit both the Site as well as the Platform immediately. Continued use will be deemed to amount to your full acceptance and consent.
[1]
https://bittrex.zendesk.com/hc/en-us/articles/360001412166]
I just assume for step to verify link to email like given an information for validiation account need permision to login... so that's why I assuming as similar like 2fa.