Lace is not on mainnet yet. But when it does come and there still isn’t support for 15 word seed phrase, I’d just create a new wallet and send your funds to that one.

Also, just want to make it clear that it’s not a Yoroi wallet you have, it’s just a Cardano wallet that can be opened with any Cardano wallet provider. I currently use Eternl and have had a good experience with it.