Can I power an interactive 'live' wall with copper tape and a 15v ac adapter?
I think it's a bad idea to have the bare copper exposed for several reasons:

Under just the right conditions, even 19 V can hurt someone.  This would take several unlikely things to come together, but open contacts on a wall make encounters far more likely, so eventually the improbable will happen.

Bare copper will corrode due to just the moisture in the air.  People touching it and adding sweat and skin oils will accellerate that process.  In the long term, this could eventually break things.  In the medium term copper "rust" will rub off on things, hurting both the copper and the thing it is touching.  In the short term it will just look ugly.

People can pick up static charges, which can be really bad for sensitive electronics when discharged thru it via the copper on the wall.