Updating the catalog is required. Your data will be migrated to a new catalog; the old catalog will not be changed.
You can do it without worry. It will create a new catalog specifically for LR CC and the old version of LR will remain on your computer as well as the old catalog. The new catalog will be named somehthing like Tom catalog-2.ircat but you can rename it to any name you like (just rename the previews as well)