Using a longer seed phrase is possible and will definitely lower the risk even more.
Note that using a seed phrase of more than 12 words doesn't actually improve the security of your coins or your private keys, it only improves the security of your seed phrase. Given that the secp256k1 curve that bitcoin uses produces keys of 256 bits in length with 128 bits of security, then using a seed phrase with greater than 128 bits of security doesn't change the fact that the private keys it derives will still have 128 bits of security.
Put it this way OP: Even if every single one of the 8 billion people on the planet were trying 1 billion different 12 word combinations every second (with no duplicates) and did this for 1 billion years, they would only have checked 0.07% of all possible combinations. It is impossible.