I've also been frustrated with some cyclists, especially now that ebikes have lowered the barrier and brought the uninformed masses onto the streets.
Here are the relevant laws in my area, just in case some of it is relevant to what you're seeing:
- stop-light - must stop, but may proceed if the light is obviously not recognizing you (local law is 90sec, but I've seen anything from 60-120)
- stop sign - treated as a yield, which means stop of there's contention, but only slow if there aren't other cars
- sidewalk - not for cyclists, and cyclists must yield to pedestrians if they use it; cyclists should use the road
- bike lane - not technically part of the roadway, and the law states that cyclists should stay within 3' (1m) of the roadway unless there are obstructions; likewise, cars must give cyclists 3' of space, so cyclists will often "take the lane" (be in the middle) of they're not getting that space
- crosswalks - treated as cars (must wait behind) or pedestrians (if crossing the road with pedestrians)
In short, cyclists:
- may use the crosswalk, but must yield to pedestrians (and cycling 15mph would certainly present a hazard and could be ticketed)
- may use the roads, but need to stay within 3' of the edge (not including bike lane of shoulder) unless there are obstructions
- may yield at stop signs and treat stoplights as stop signs if they don't change for the cyclist