I have an '06 175 Opti on a wheel boat, I have a kicker too though so I don't troll with my Opti. But it idles at 550 rpms and I would think if you propped it for trolling and especially if you went with the SmartCraft gauge that lets you bump down the rpms, I think you'd be good. Should be pretty similar to your 135 since they're the same block.
My Opti isn't propped for trolling so I can't give you any help with speed, but when my family goes cruising we close the throttle down and idle around a lot, and the motor never skips a beat.
From what I've heard and even experienced first-hand, a big 4-stroke will NOT troll down as slow as a big DFI motor like the Opti. But the Suzuki's gear ratio should help you slow down if you go with that motor.