When you load songs into Jaikoz, the files metadata is held in memory, and a row is added to the main spreadsheet browser for each song. So adding more songs use more memory and gives the graphics processor more to do because the spreadsheet browser has more rows to handle.
Jaikoz can handle upto 20,000 songs okay but after that it may struggle. If you have a really large library it is best to only add the section you are interested in, if you need to process all songs in one go then SongKong is a better bet. SongKong works on a folder by folder basis only uses memory data for the folders it is currently processing so can be successfully applied to libraries of any size.