OK if using standard lugnuts, assume your new rims are YO 15x8". I'm not aware of any extended version to suit those, could be, haven't seen them mentioned, whereas the others came up several times. X2 longer studs may be the way to go so you still end up with stock length to mount on. Pulling axles isn't too hard, as hard as draining the diff oil and removing C-clips, possibly be more work removing rear disc setup.
I guess the rear disc conversion should have mentioned the likelihood of further mods being required, and if your rim is that far out it likely isn't mounted anywhere near the hub for centering the rim. I think factory rear disc cars used a different axle for this as well. Depends what conversion you used, I'd start there. Focus on the cause, is it a rear drum/axle setup with disc rotors slipped on that are far thicker than drums?