Make sure LW is using Java 1.5. You can verify this: Setting up Java 1.5

Other techniques to lessen the Java burden:

Only keep whichever windows open that you need at the time. Close off old search tabs if they've been there a while. Keep LW hidden in the dock whilst you're not searching. After opening LW wait 10 to 20 mins or longer before using. Let it settle down 1st. Go to LW's prefs>Speed & tick disable Ultrapeer Cap. & press apply button. Set both uplds & downlds to autoclear.

Don't use the Resume/Find Sources on all your files at once. If you use it, do it one 1-3 at a time.