Wow 15 years? Amazing. You will see lot of changes specially pollution and A LOT of people. It will be overwhelming for you for few days but after that you will get used to it. First thing you will noticed will be the airport. A unique dirty little airport. You don't have to look for any sign for the direction( if there is any). Crowd you lead you to the terminals. I would say you will love the visit. I have been to almost all the states in US but couldn't find any better unique place than Nepal.
Good luck to you my friend and enjoy your visit!