Using wav files makes this harder, because that format can't have embedded tags. You either have to rely entirely on the database, or give the files names that contain all the info you need to transfer. That's a project, and fraught with traps because file names can't be as long as tags/fields, can't contain all the same characters, and might not retain desired capitalization.
Assuming you are using wav to preserve maximum quality, consider using MC to convert to lossless flac or ape (or max quality mp3 or a few others), formats which can have embedded tags, which you can embed (library to file) using MC14 then extract (file to library) using MC15.
But, why not load a backup of the MC14 library into MC15, thereby having the same database records pointing to the same files? No need to import to create a new library. You have to use a MC14 backup --> MC15 restore because the actual library files are not compatible. By using the same library (database), whatever you have in MC14 as track data (and views and other good stuff) you'll still have in MC15.
You won't yet have bolted together the data and the files via embedded tags unless you use a different file format (or perhaps in the future you can use MC15's sidecar mode, which right now seems to be only for video files). Again, there are other ways to go, depending...
As to missing data, you might get lucky with online lookups, otherwise it's just a lot of typing.