How slow is it? When you're making maps and stuff, there's no people playing, so I guess cause of that it's faster.
Um, try being places with less people. Also if your computer's older/slower that could be why.
There's a few things you could try that may or may not speed up your game.
On FeralHeart, lower your viewing distance
On your computer, if you go to the start menu and search "Disk Cleanup" and "Disk Defragmenter" These will both get rid of unneeded files and clean up space on your computer, which is good for it whether it helps or not. They won't delete any of your stuff, so that's not something you have to worry about.
