"I would normally think that a lighter bullet, say 200 Grain and higher powder load would produce a flatter trajectory, hence more accuracy."

I don't know where peo[ple get the idea that a flatter trajectory which results from a higher velocity somehow equates to better accuracy, because it DOES NOT!! The only possible advantage would be that hitting is easier if you don't have to be as precise in estimating range and holdover.

Despite the fact that they can be launched faster, lighter bullets suffer from some possibly significant disadvantages too. One, they may be too short for optimum accuracy from the twist rate your particular rifle has. In addition, although they start out faster, they also shed velocity faster, and may therefore have less downrange energy.Also, while their short-range trajectory may be flatter (the best of all in this regard is the round ball), further out, their trajectory becomes quite steep due to the rapid loss of initial velocity. Lastly, the lower sectional density of a lighter bullet reduces thge buillet's ability to penetrate,limiting the angle of the shots you can make with it.

IF you are getting 1.5" groups from your present bullets, I think that's great. I don't know if a lighter bullet would do as well, but a bullet heavier than your present oneis just as likely to improve your groups as is a lighter one.