Remove gloss paint from plastic soffit vents

I'm getting the soffits and fascias repainted next week, and have a number of rectangular plastic soffit vents that are looking a bit worse for wear after having been painted over by sloppy painters in the past. I've removed one (it's a bungalow so easily reachable) and managed to get the paint off by soaking in a bucket of hot water overnight and scraping it off with a combination of a flat blade screwdriver,my fingernail and a stiff brush.

It was relatively easy to do, but the prospect of doing another 15 or so begs the question of whether there might be another option. I'm fairly sure it's water based paint, so I'm thinking there might be something I can add to the hot water to expedite the process and/or make the paint easier to remove. Or would some kind of solvent work (even though it's probably water based)?

I can get new soffit vents but they're €7.30 a pop, so don't really want to go down that route.