In my experience the amount of evidence depends on how you met. If your partner is a hooker whom you met in a tourist bar, the night after she got out of prison, your relationship might get questioned. The counselor officer asked my ex-wife and I how we met. She was a speech-language pathologist, I was teaching a seminar about treating childhood stuttering. The counselor didn't asked any more questions, flipped through our photos in two seconds, and approved her visa.