2-stage triggers are usually a HUGE improvement in trigger feel.

Trigger pull (actually, trigger torque) is a combination of the springs, plus the friction of the sears rubbing. In the M15/AR-15 design, the sear is very close to the hammer pivot, so the hammer spring has a huge mechanical advantage in loading up the sear force, so the friction is very high. That, plus the sear is far from the trigger pivot point, so the friction has a huge mechanical advantage in creating torque you have to overcome.

The 2-stage triggers move the sear much further from the hammer pivot, towards the trigger pivot, so you reduce sear loading, and you decrease the mechanical advantage of the torque. Net the friction component of the pull force is much reduced.