It definitely is way oversized for any kind of rec diving. People only started buying these after all the facebook and online marketing started and every noob wants to dress up like a cave divers... same reason why people buy 1500 Euro canister lights and 'tec fins'. It's mostly to look 'tec'/cool not because it makes sense... and it makes more money for the shops. 15 liter tanks are great for OW diving.A 12+12 litres here is already considered something "tech", a bit oversized for recreational diving.
Remember that the OP was not interested into deep technical diving, but just wanted to extend his diving time for standard recreational diving.