Do I really need the BTR15?

Hey all I’m just starting out with IEMs and recently got the KZ Castor Pro (2DD version). I'm currently using them with a Hiby dongle DAC (the entry-level one). I’ve seen a lot of talk about the FiiO BTR15 and was wondering… do I really need it?

Would I actually notice a big difference in sound quality ?

Appreciate any advice.. Trying not to fall too deep into the rabbit hole (yet 😅).