Not only is this achievement difficult, but VERY frustrating too. Simply because if you get to a late stage in the World Cup such as the final and you lose, you will need to do it all over again. Plus, it is very hard to boost as you will need quite a few people to be very patient.
Firstly, the best 1.5/2 star team to be in my opinion is New Zealand. They have a very decent centre-back, Ryan Nelsen and a few good attackers, one being Smeltz. That being said, the best formation to play with them is the 4-2-3-1, with Smeltz playing as striker. This formation is very effective because you have two defensive midfielders, one of which can go forward if necessary, two wide players and a centre forward. This formation is perfect for a team like New Zealand as you can counter attack teams that are similar ability to yours very easily.
The most important thing to remember when going for this achievement is to not play against good teams. When your in the menu searching for an opponent back out if you get put up against a 3 star team or better. Sure, you may be able to beat some people with good teams but its defiently not worth the risk, especially if you lose. Because New Zealand are quite good at being a 2 star team - as they have a few decent players, you shouldn't have too much trouble beating worse/equal teams to yourself. That being said this achievement is mainly due to your skill at the game, and if your not too great at it, then you may not be able to get far in the tournament.
There isn't really much more advise I can give other than the team to be really. Its a tough achievement, which really depends on the player's skill more than anything. Just don't forget to play teams that are equal or worse than New Zealand and don't forget to always play on a connection that has green bars! You don't want to play on a laggy connection that you can't do anything on! Just remember those points I have made and they will certainly help, and good luck!