If you are just speaking about symmetric encryption yes of course it's going to be much faster. The same reason most of the world (TLS) uses it after doing a key exchange. The goal of nip04 and 44 was to bring "asymmetric" encryption using ECDH. The key derivation part is expensive. EC is typically far more computationally expensive than most other forms of asymmetric encryption, obviously depending on the data size. Large blocks can have better performance over RSA because you're using a symmetric cipher.

You're still generally going to want to generate IV's and store them with your data.

Finally, unfamiliar with Postgress, but it's generally bad practice to use your own encryption functions if the DB offers encrypted columns. Most SQL implementations do.