Next thing to try is deleting your LW preferences folder. http://www.gnutellaforums.com/window...ng-should.html see post at bottom of thread about how to save your previous incomplete downloads.
Also try changing compatibility mode (a few options to try) & Run as Administrator, points #5 & 6 in above link. Can also make Java run in Admin mode. Search computer for Java.exe, right-click & choose Run as Administrator. This might help (is mandatory for Windows 7.)
(All the above tips need to be done whilst LW is closed.)

Do you still have incomplete files from long ago? Might actually be wise to remove/delete these if too many it may be making LW struggle.
Do you have lots of files sharing? Might be wise to start with less initially until your LW starts to run properly.

I presently share 6-10 thousand files, have shared up to 16 thousand with LW 4.

It sounds like you are using LW Pro? Or LW Basic?
If you wish to remain with LW 4 (many do), then you could perhaps try downgrading to LW 4.16.7. But there is a trick to do this properly to retain your previous downloads history. Else you might try the LW 5 series, such as LimeWire Pirate Edition (LPE.)

From what I can see from your description, Java is struggling with memory. This suggests settings that are causing a high memory use-age. Memory use-age problem might really be due to various things.