Not that I necessarily agree with jeremiah's advice, but if you can't possible throw a 150 class disc, that does indicate form flaws that heavier discs tend to mask. You get good distance, but would probably get better distance if you worked to eliminate those flaws, likely including some OAT.
You can't possibly throw a a 150g disc with the same power and snap as you would a max weight disc and expect you get anything close to flying flat or str8. Just the power and snap alone accompanied by how light the disc is would, evey time, flip it right over into the ground.