Can I fire .222 ammo in my .223 to fireform the brass to .223 dementions. I realise that by brass will be 1.5mm short initinally.

In a word No!
Way too much difference in case lengths.
The 222 case would leave virtually no neck if fired in a 223 chamber. I would think it would take a controlled round feed action to get it to fire, if you could get it to fire at all.

muck

If you have .222 brass find someone with .223 brass that will swap with you.

If you have good brass you should be able to trade it off easily.

223 brass is in great supply and cheap too!

.222 brass fired in a .223 chamber will usually rupture and send hot gas back thru the action. And the results aren't worth fooling with.....
Don't ask me how I know.