Can you fit 15x9's without flares? What kind of offset would be ideal?

15x9 0 offset will fit but you will probably have to stretch the hell out of some little tires and roll the fenders.

15x9 0 offset is do able for the rear without flair but like above said you need the roll the hell out of that fender lip and pull like crazy the. Use 205 or below... Now for front 15x9 same offset not do able unless you rock some crazy negative camber and crazy roll/pull and trim/remove inner plastic guard.

It can be done. 195/45 stretched on a 15x9 with a slight fender roll.

I'm running 15x9 -15. I'm also running 175/50 (super stretch). No body roll or body pull.

175/50 is a **** size on a Corolla in general, let alone on a 9" wheel. If you want to run 9's either flare the metal guards so you can fit sensible sized tyres without massive amounts of negative camber, or get bolt on flares. It won't steer as nice as it would with narrower wheels anyway, do you want them just for looks or do you actually need a wider tyre?