this is an extremely brief problem description ... you might get a better answer if you gave us a lot more background
But the extremely brief answer is: you should upgrade the elements catalog (unless there's some important detail you haven't told us, so who knows what the right answer is)
How long would it take to create a new catalog from scratch ?
There is no risk in trying a catalog conversion (update) and it's reasonably quick.
- To 'update' PSE12 catalogs you need a recent version of LR (5.3 or 5.4 I think).
- If you have been using the new tag categories (people, places, events) and people recognition, I don't know exactly how that will work, since I don't use those features.