An outdated or corrupted graphics driver can also trigger the out-of-video-memory error. If your PC meets the system requirements for Fortnite but this error persists, you need to update your graphics driver to see if you can resolve this issue.
Just because its a Titan doesnt mean this cant happen. Do a complete reinstall of all your graphic drivers. Make sure they are fully up to date. When it asks you to do a clean install select that.