Painting - factory primed steel door paint removal

I painted a Factory primed steel door with oil based paint (which took a LOOONG time to dry) then found I was supposed to use latex paint. Now I want to remove the oil paint and use the proper latex paint. What should I use to remove the oil paint? Should I remove it???

I would first determine why the manufacturer recommends latex paint. Depending on the reason, I would either leave the oil paint on for now or remove it with a paint remover. If the paint remover takes all the paint off down to bare metal, then you'll need to reprime the door before applying your finish coats. So you might also need to find out what type of primer the door manufacturer recommends. That's how I would approach it but I'm open to other suggestions.

Generally, the manufacturer recommends latex paint due to the expansion and contraction of such a large homogeneous surface. Alkyd paints oxidize to a hard, inflexible film likely to fail because of the expansion and contraction. Latex, on the other hand, is more flexible because it dries and amalgamates.