Taking search times into account due to the population not being at its highest, you only being level 2, and assuming you don't just have free time 24/7, the 152 grind can take you a pretty long time. Not trying to discourage you, but you've got some odds stacked against you.
If your goal is to hit 152 before Infinite drops, you've got quite the challenge ahead of you. Firefight definitely helps, as it rewards tons of Gold Req Packs pretty early on. Gold XP packs were a godsend too, but they don't really hand those out often, and cost real money to always have.