15x6 with 215/65x15 is a good choice.
16" wheels are a bit too large and 7" rims a bit too wide, give a hot rod look which is not in keeping.
Fitting 215 tyres to a 6" rims gives plenty of tyre sticking out past the rim so you are much less likely to kerb your expensive rim.
You can fit 215/70x15 tyres but almost all of them are for transit vans or similar, low speed rating and very square edges.
215/65x15 130mph rated tyres £165 for 4 delivered. item no 173290903435
The 215/65 tyres give a retro ride feeling, you can feel them twisting and torquing up if you put your foot down. It makes you realise how much more grip todays modern low profile tyres have.