If you are using a hardware wallet, you will not be given a 15-word recovery phrase by Yoroi because your Ledger holds the private key needed to access your funds on the blockchain. As long as you have your hardware wallet (and its recovery phrase), you will always be able to access your ADA and make transactions through Yoroi.
I installed Yoroi and successfully integrated it with my Ledger/Trezor, but I wasn't shown my 15-word recovery phrase during the wallet setup.
