I dont see any benefit in getting rid of your current rifle to trade in on a M&P15T. I think you would be better served selling your A2 Colt upper, and getting a new upper receiver built up how you want. A 16" Stag Arms M4 upper built up with similar components that are used on the M&P15T would be a great set-up, and not to mention it is manufactured in the same factory a the S&W M&P15's. It would cost around $850 to build the upper.