There are a lot of differences between Search (Find) and Filter. Filter only works on the current folder. Search starts on the folder pointed to and works it way down the folders to the end.
With search you can add multiple search lines and add include all or only or to give you some logic to the search.
I have spent some time creating a keyword system for 15000 photos
Like Curt says, but after all this work make sure you have a proper back up of your keyword list. Use the tiny little menu icon top right in metadata panel and choose export to create a copy of your list so you can always revert to it using import in case something bad happens.
And with those keywords written to the files in the IPTC many other applications (or clients) can read and search those keywords