The .exe for my game also states it is from 2015 though I've downloaded a newer game. It is likely that 2015 was the first time Runey created a file named Harem_Hotel.exe and changes to the file have not updated the create date.
The default folder name for Harem Hotel should have it's version number in it and the version number is also available under the info selection of the options screen in game. Check you version number and if it's less then 0.8 you can download 0.8 here on itch.
I don't know if there is an update utility but your saved games from previous versions should still be available even when downloading the entire thing over again (granted that the newer version doesn't break older files which I have not yet encountered with this game).