Turn Rate vs. Load Factor comparison
Rookie,
I am not a pilot, but have spent my career in design of flight control systems. I am very familiar with flight mechanics. A quick look at a little physics/math might help your cause.
The the heading rate during a turn scales with the tangent of the bank angle. (Turn radius scales with the inverse of the tangent of the bank angle.) The steady normal load factor during a turn scales with the inverse of the cosine of the bank angle. It is interesting to compare the two bank angles available with your autopilot:
Bank_ Tan_ 1/Cosine
15 deg 0.27 1.035
28 deg 0.53 1.133
From these data you can see that increasing bank angle from 15 to 28 degrees does not quite double the turn rate (or not quite halve the turn radius) while it increases the incremental load factor by almost a factor of four! (1.133 - 1) ~= 4 * (1.035 - 1)
Where your flight operations permit a half rate turn the payoff in reduced load factor change for your passengers seems well worth it.
I hope you find this comparison helpful.