If I get my cars geometry sorted out while I still have 15" Rims on it, will the settings be correct when I replace them with a set of 16's shortly afterwards?
Bit of a dim question I know but there you go.

 

Not a dim question at all.
If the 16's /tyres are the same rolling diameter as the 15's /tyres there will be no issues! (assuming you use the Subaru off-sets).

911

 

Ok now for a really dumb question what are offsets? Oh and also what is rolling diameter?
I have no idea at all!

 

Wow!
Offset is a dimension marked on the inside of the wheel cast spoke usually which accureatly gives the distance in mm from the mounting face of the wheel (to the brake disc/wheel stud )
On Impreza's this is very impoetant, and will restrict the options available to you. If you stick to the Subaru wheels ie the P1's you are ok.

The rolling diameter is very simple. it is the diameter of the inflated tyre. For the Impreza it is about 610 mm or a bit more.
If you fit the P1's with the correct tyre size the speedo will work perfectly accuratly.

The 17's do enhance the taut feeling of the chassis response when changing direction due to the lower profile tyre wall, and they look Gooood!

Impreza's work well with certain makes of tyre, Toyo, Goodyear seem to be the favorites. There are other more specialised tyres, but the above are good all-rounders.

There is a set of P1's for sale NOW in the General Sale section of the Snet, £450 is a good price.

Hurry!

911