A factory reset will certainly return your device to its original running speed, but if you don't want to lose all your saved data, you could try clearing the cache and running apps in the "applications manager" under settings.
Sure , you can do a factory reset to free up your tablet sapce. But you'd better back up files on your computer. If you lose any data after resetting your device, you can use Data Recovery for Android to restore your data. Good luck!