Options I can think of are (a) disabling some of the advanced features, (b) reducing incomplete files, (c) reducing shares if many, (d) making sure Java is up to date.

(a) Disabling ultrapeer, DHT & TLS options are found under prefs -> Advanced -> Super really Advanced -> Performance.
(b) With LW 5, incomplete files can be removed by simply canceling the downloading file.
(c) Too many image files in Library can slow LW down considerably. Next culprit is audio files. Simply control-click file in library to remove from library.
(d) Check OSX's Soft. Update tool.