I wouldn't go anything less then 1500, 1200 is pushing my boundaries for extreme cases. I would stick with the 1500. if the touch up paint has a clear additive then it is probably harder then other types of touch paint. some types of touch up paint is softer then others when it cures. i would try tar and wax remover and a rag first try to remove as much as you can.
you have to becareful when wetsanding touch up paint, because you have a natural tendency to keep wetsanding one area till the touch up paint is gone to your likeing, but the problem with that is you can easily wetsand through the "good" surrounding paint, then you have just created a hugh eyesore. same goes when polishing, you might wetsand to the point that it does not burn through, but as soon as you put a buffer on it then you soon find out that you did now.
try the chemical first, less likely to do more damage
then you can try the wetsanding part.