There are many lemmy instances in the world, but currently most people are using lemmy.world. This is why everything has gotten so slow.
You don’t have to delete your lemmy.world account, but check out https://lemmy.fediverse.observer/map it’s a geo-based map of lemmy instances – explore stuff nearest you, pick one, sign up, search , subscribe and begin interacting with your favorite communities. It’s easy, free and it will be faster. Try it!
Yeah do whatever you decide is best! No right way to do it. Some have suggested just considering accounts temporary as we all experiment with what works best until more features are rolled out. But I know I’m already attached to my existing accounts and reluctant to make more.