How Does DB15 Support Work and Is It Zero Lag?

[metal_slugger]

Hi
I do not have any SNAC adapters, so far I have been using recommended USB controllers for low lag, plus I own an IO Board v6.1
I have noticed a few arcade cores offer DB15 support, like the recent "Nemesis (ROM version)" core.

Can someone kindly explain to me
1) How DB15 support works and does it offer zero input lag like SNAC?
2) What equipment / controllers do I need to use it?
3) Can I use my IO Board v6.1 as the interface?
4) Does it also work with console cores?

Thanks!