You can also just participate once every consecutive 24 hours in a league race. So no need of swapping leagues for doing more races. Changing leagues is better advised if the competition in your league becomes too slow for you or their ain't enough league members.
If you are looking to level up faster, find a league with a player who has a high manager level in your tier. You gain more XP the higher the difference between your manager level and the highest-leveled manager in your tier.
You are limited to 1 league race every 24 hours so no point swapping leagues to race more; your design is also reset when you swap leagues in the middle of the season.
So in short it takes a looomg time to lvl up ah?
Patience is a virtue:)
Cheers
It should take you a lot less time. Take the time to read the guides that experienced players have made available in this topic to everyone to minimize struggles and frustrations. As you can see this forum is a great source of information.