plumbing help? copper pipes?

Kippy is correct. The di electric union prevents a corrosive reaction from occurring between the copper and steel by isolating them from each other. It is the correct way to join a non ferrous metal to steel. The union is readily available.

try a wet vac yo suck all the water out of the line make sure you have the main shut off and a faucet open and if you still get a little water use the bread also does husband know how to solder clean the pipe and joints use soldering paste if it is 1/2 pipe all you need is about 1/2 solder heat fitting until solder melts by touching hot fitting not by the flame of the torch

could "just over an inch" really be 28mm - in which case you need a 28mm-22mm brass reducing connector a short length of 22mm pipe and then a 22mm-15mm brass reducing connection I don't think I've ever come across a 28-15 reducer in one fitting - if you can find one that's what you need but otherwise it's two joints I'm afraid.

You should use a brass connection between steel and copper. If the ends were threaded, I would say use a hydrostatic union.

Have a steamfitter or a plumber do it for you. It won't cost that much. It's probably like a 10, 15 minute job.

You will need two compresion Connectors.

You need one to be one inch to three quarters, and another one three quarters inch to half inch (15mm) Use copper pipe between the joints about 3 inches long.

brass connection between steel and copper

water pipes a measured id ,inside diameter or bore ,you should be able to get a compression reducer adapter from the large pipe which i think will be inch bore to the 15 mill pipe

You need a di-electric compression union ask at the hardware store.

nosdda answer is a correct standard way of doing this job so rated the answer.