Like I said, I'd be happy with just five gold for taking it. I know the poison bit is REALLY hard to balance between "useless", "useful", and "stupidly good." Even if the only time I ever used it was a place to drop all my spare piety before leaving a dungeon just for a few extra coins, that's still more than I use it now. It would be _nice_ if the poison effect could be more useful than "about one single full heal" but I'd understand if they didn't want to fool with that at this point.
Or they could slightly decrease the piety hike, I guess. 15 + 8n or 7n or something. Yeah, it's not neat multiple of five like most everything else, but a couple of extra shots earlier on might help more. The gold's probably safest. I mean if you have 75 spare piety at the end up a run, surely 15 gold is at least "better than nothing." It's not like you get any gold - or anything else - for unspent piety at the end of a run.
(Sidestepper is correct though. We really should have said something during Beta to get poison changed to something else entirely if the devs were willing. It only makes sense from a flavour standpoint; mechanically it actively encourages you to do something TT will punish you for, unless you specifically use it as fireball spike, stab, regen mana, fireball one more time and _maybe_ the poison was enough tiles so that they didn't regen over your fireball damage.)