Users of V-Ray 1.5 for Rhino can download a free update from the Chaos Group Downloads page. The update features improvements and fixes that make V-Ray 1.5 for Rhino more stable and responsive:

• More stable DR
• Made RT more responsive to Rhino events, removed unnecessary refreshes, and introduced "lock viewport" option
• Fixed scene upgrade issues
• Improved scene loading time
• UI improvements

Check out the full list of improvements and fixes and download the free update!