VTR's are reliable if you look after them, treat them like shit and they will treat you the same.
There is a slight engine difference beetween the faclifted model and the non-facelift. The newer VTR's with the grey engines have 98bhp were as the old ones only have 90bhp. The facelift is just new lamps and different insides really.. Nothing special. Must admit though the non facelift model looks allot more aggresive than the new one. I dont think any suspension tweaks happened though.
On 15's youd probally be best going down around 40 - 50mm, i dont think that would involve much archwork, depends on the profile of your tryes really. My VTR is ok for petrol buddy but if you do tend to drive like an arse it will drink it
Best suspension you could get would probally be an eibach setup or a blistein setup but there expensive... look around for something cheaper if your on a budget. I have an Avo/Eibach setup and its brilliant.
Edit: If your buying take it for a test drive and listen for squeeks and shizzle... saxo's are renowned for being tin cans
not that i want to put you of getting one.