It depends on the consulate, can be 2 months, or 2+ years. Is yours Vietnam? Just guessing from your profile. But if so, it's super quick in Ho Chi Minh City.
@Sarah_k92, London is about 5 months for an IL now, the backlog has increased. So you should get an IL about July time, probably for an interview in Sept. You can keep an eye on it here - https://travel.state.gov/content/travel/en/us-visas/visa-information-resources/iv-wait-times.html