Library too big

I've been working on a project over the last three years and the accumulated media seems to be slowing things down.  I capture all the media externally so the library itself is a manageable size, but loading the library takes a while and it seems to play more slowly than my other smaller projects.  I'd like to split the library or at least start a new one to run concurrently with the original one, but I'm not sure how to go out doing that.  Any suggestions?  thx!