Pages Freezing

I create and sell teacher materials for an online teacher store. All documents are created in Pages then converted to PDFs and JPEGs. Since updating Pages a year or so ago, it freezes when the document gets heavy with graphics. If I click to move a graphic and hold down the mouse for 10+ seconds... the beach ball appears! Please help if possible. Using... OS X Yosemite 10.10.3 I do not know how to find Pages version... pretty recent. My computer was purchased in 09 and I've done my best to "clean it up". Any advice would be helpful.