You can brighten the players lights by right clicking on the root template "Player_Light", clicking edit, and increasing the intensity on the side bar.
But I think the ARX_HorrorSleep_Cave_PitchBlack is too restrictive. It has some gnarly distance fog and I think that's part of your visibility problem.
I would try something like ATM_PBR_Default_Cavern_G or ATM_PBR_Default_LV_LowerDeck
You can also go to the resource manager and try to edit the atmosphere settings of the one you want. I haven't played around with editing atmospheres much in D:OS 2 though so I can't offer much help there.
