Why is Pages 5.5.2 so slow in Yosemite 10.10.2?

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I have used Pages in other versions for a few years and prefer it to Word until now.  Over the last few weeks when I'm trying to write assignments, I keep getting a spinning ball which takes anything from 30 seconds to 3 minutes to go away, during which time I can't use Pages at all.  This isn't exactly good for writing flow.  I don't seem to get a spinning ball elsewhere e.g. messages, mail, etc
Peter, I have only a 3 page document.  All drawings yet, quite simple (the type you'd see in patent art). I'm currently running Pages 5.5.2 on a Macbook Air (c.2012) 1.8 GHz, 4G RAM, 20% free hard drive space.  Moving, copying, pasting shapes is quite slow.  Even scrolling the document is slow.  Looking at my activity monitor, %CPU for the App ranges from 0-99% (seems most intense when scrolling, copying or pasting).
Total number of shapes/lines/objects: ~100 (many are grouped to reduce individual parts).
Any suggestions on how to improve this?
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