Only for metal parts. If time is important. I assume you are over 18, you will need to be to buy this.
Dichloromethane. It is what used to be the active ingredient in most paint strippers up to 2009 Nitro-mors ect. It is illegal to be sold as a paint stripper in the EU now, but can still be purchased very easily for other applications. I get mine from a local model shop that sell it as a type of plastic glue. It's dirt cheap in most cases. If you ebay it you should be able to get 1L for £2 or somewhere there about.
https://www.youtube.com/watch?v=ds6QixjSy5c
https://www.youtube.com/watch?v=T0-WrD5ckh0
https://www.expotools.com/cgi-bin/sh000005.pl?WD=plastic weld&PN=Plastic-Weld-PW.html#SID=175
Warning, The stuff is super aggressive, will eat any of the thin medical style gloves. Work outside, Work with thick industrial gloves. It will destroy anything made of plastic so don't even go there for plastic stuff.
It'll remove most spray paints in a few seconds with a dampened cloth and just wiping, the paint will dissolve totally in a lot of cases. Dries near instantly, And can be repainted over after a quick wash in soapy water. It is the single fastest paint remover I have ever used period. Cleans right down to the metal instantly and has very little clean up time as it's a potent degreaser as well.
I did a motorbike fuel tank with the stuff, Took it from hard clear coat to bare metal in about 30 mins without any hard scrubbing or sanding. I also did an M4 I picked up the other day with it. 10-15mins of gentle wiping and it was back to bare metal.The stuff is very hard to beat.
For plastics.
Fairy power spray. Spray on, leave it 10 mins and rub off the paint. Doesn't work so well on glossy finishes.
Detol is also good but I find it too slow, and on etch primer it'll be sketchy at best if not left for a long period.