Site performance

Since installing WPMU plugins I have found a considerable loss in speed on my site. In fact everything is slowed down. Just to go from page to page takes about 5secs. I am on the trial version so would like to know I can fix this before committing to pay. My issue is also that when I try to use Smushing it doesn't save my configurations and it hasn't smushed all the images in my media even though i keep clicking on the button to do so.