in order to measure the offset you need to turn the wheel upsidedown and measure from the back of the stud holes to the outer edge of the rim..then do the same for your alfa wheels currently on your car, the difference between the two (ifany) will give you the spacer size needed...the PDC (stud pattern) will be the same for fiat/lancia and alfa.(four stud only)
I have a set of thema wheels on the black one and they hit the front calipers but this having said this it is a wibebody so bigger disc's and calipers and i see you have a skinny so i don't see any problem.
Just make sure they are the series 3 alloys 15" and not the series 1/2 14".
I have just been told the Dedra have a different offset.
I think you can by the alloys for £55 each brand new so don't get ripped off.
I know about these we have 4 in the family.