From the original blogpost by Carter Chanklin:
We’ve added 32 new cmdlets, enhanced our existing cmdlets, and fixed tons of bugs. If you’re the sort of person who loves fine print, you can also have a look at our release notes. The release notes has a great table that shows all the differences between 1.0 and 1.5.
More info and videos can be found in the original blogpost: http://blogs.vmware.com/vipowershell/2009/01/vi-toolkit-15-released.html