Slower is definitely less safe when riding near motorists. The speed differentially alone will magnifiy any impact.
35-22 = 13 mph impact
35-15 = 20 mph impact

On 25 mph arterials like Hawthorne, 20th, and 28th I typically take the full lane. In other words, you will find me in the middle of the lane ~1 meter away from the left. If I am on a fully loaded grocery bike and can't maintain ~20 during a climb I move over to the right (e.g. 1 meter off the curb). On Sandy and Burnside there is a wide lane and shoulder so I ride on the right (1 meter from the curb).

Its pathetic that Sandy and Burnside have stretches with 35 mph speed limits. IMO, every non-limited access arterial within PDX city boundaries should be lowered to 25 -- and some to 20.