I presume you are using the latest LW 5.2.13 version? LW 5.2 will reduce drag on the system compared to LW 5.1

Try not to gather too many incomplete files. Make sure your Java is up to date via Software Update under apple menu.

Go to LW's preferences (command-comma) -> Advanced -> Super Really Advanced -> Performance, & Disable Ultrapeer mode, Mojito DHT & TLS. See if that helps.

You could set up a Test Account on your computer (easily created, easily deleted later) & see if it also freezes in that account. But don't have both LW's running at same time of course. Setting up a Test Account in OSX (click on link). If no problems, then it might be a good idea to delete your old LW preferences. Before doing that, make a note of all important LW settings, then close the program. Find your LW preferences folder, remove the Downloads.dat file & put it somewhere safe. Then trash the LW preferences folder. Now open LW & see if it behaves any better. If yes, close LW down again. Then go back to your new LW preferences folder & put the old Downloads.dat file back in replacing the newer one inside. Now you can re-open LW. Deleting LW Preferences folder in OSX