It is logged on the JIRA as https://jira.secondlife.com/browse/VWR-26182 - and is apparently fixed from Viewer 2.7.6 onwards, when that reached the main viewer channel.
If you find Viewer 2 running slow on a laptop or netbook you will probably find that Rainbow runs faster - please note that it is based on Viewer 1 so it's look and feel may not be so familiar to newer residents.