To keep it simple: Yes, if you have 230VAC and the load wants 15VAC, you only need a 230VAC:15VAC transformer of appropriate size.
To also keep you safe, you want a fuse so a fault does not heat-up your line cord, set the carpet on fire, burn-up your house. And a box so your child/cat does not touch live wires. You may also want a switch. In some lands a commercial product must use a 2-pole switch. If the box is metal (plastic boxes should be Approved for hiding live wires, so not a cookie-tray) and you have a 3rd pin (PE, green wire) on your wall outlet, there should be a substantial bond from wall 3rd pin to bare metal on the box, so a loose wire will blow the fuse in the basement before anybody gets shocked.
A transformer rated for 15VA (15V, 1A) will not burn any house still under shortcircuit conditions. The finest of the primary winding will act as a self fuse. In any case, external fusing and or a thermal cutout is recommended.