Have a look on here
www.mytyres.co.uk
You have to buy either pairs or full set of 4 but look at the prices - you can pick up budget tyres with no real brand for silly money.
Check them out before buying part worns.
As for VTR rims these are the wheels all 8v VTR Saxo's same with out of the dealerships all them many moons ago. They are a 14' wheel that are 6'wide and take a 185/55/14 tyre you can go super low with 14' rims with no real tyre rubbing until your touching the tarmac
15's are the best all round size for Handling, looks and the ablity to lower nicely without to many problems. Later 16v VTS's came with a 15' alloy twisted 5spoke with a wider and lower 195/45/15 tyre.
Id go for the 15' as they really do sit well with the car and will bring your car down out of the clouds.