Here is what I gather (some may not be true) and some of my opinion:
1. Yes you can get a ticket for 25 in a 15mph zone and this is even more likely if a school zone
2. No you are not required to show ID or DL, but you are required to correctly identify yourself.
3. An officer can detain you until you show ID you if they suspect that the ID you have verbally given is false.
4. You will not get a ticket for 30 in a 25mph zone, same as if you are driving, the margin is too small.
5. You can get a ticket for reckless cycling (i.e. unsafe speed for current situation) no matter what speed you are going. This means you could get a ticket for going 25mph in a 30mph zone if there are unusual road and traffic conditions.
6. You should obey the traffic speed laws, not because of fear of a ticket or fear of the law, but to be a good respectful road user. Just as you don't want cars speeding in your neighborhood or on roads that you cycle on you shouldn't be that cyclist who speeds thru low speed zones and puts peds and others at risk. There usually is a reason for 15mph zones.

Al