If you’re a newbie and learning the sport I would say 15 mph maybe 20 max. This is if you are new and learning normal sight picture, trying to get consistent, and learn the game. Once you are getting better and trying to compete, wind is your friend because if you can shoot in it and your competition can’t... well that’s where you’ll stand out.
It’s like any sport though, if you are starting out, you want to get consistent and get the basics down well and that’s better with easier conditions. Once you can smash them pretty well on nice days, it’s time to head to the club on windy days and start increasing your skills. The fact is, you MUST be able to shoot in wind if you can’t you won’t be personally satisfied even if you only shoot for fun. Windy day shooting does really force you to watch the target and fine tune that ability.