
Just have some random battles in the field, you'll defeat 15 monsters in no time. If you haven't started it yet then you'll still reach 15 kills although it will take a little longer, it's pretty easy though so you shouldn't have any real problems.

Can this be done on either version of the game? Started it on PC and since I already have progress on the PC version I’d love to just do it there if I can

Reach the house, turn around the entrance to the second window, enter and try to open the doors, leave the house and do the tutorial battle, after that you go to prison, do all encounters you can here, in 10/15 mins is done.

Do any achievements pop for this if you haven't started the game yet?

killed 15 ennemi, no achievement unlocked.
When you kill an ennemi you can leave the area and come back, ennemi respawn

You will not get an achievement if you do this. The first possible achievement in the game involves doing a certain task on the first boss fight. You would definitely have defeated 15 enemies by the time you reach it.

I think it doesn't work on pc 😩

Leaving a room and re-entering regenerates enemies you've beaten so you don't have to walk around looking for enemies.

Did more than 15 kills on PC and doesnt work.