Using Rift, strong myopia (about -10) myself. Started VR with using an older set of (general purpose, single focus) glasses, because the frame of my most recent one was definitely too big. It worked, to an extent. But still no comparison to the prescription lenses I ordered.
You should note that on ordering the prescription lenses it asks you for the values of the glasses used for far sight, not your reading glasses. And in case of bifocals, to leave out the "Addition" values - they describe the change to be done for the "near" part of the lens, in relation to the default value.