I think 15mph makes a lot more sense having ridden at 8mph.. the Scooter is barely stable at that speed, but yeah limiting cars to a speed that's more like 2-3x that rather than 5x would make the slow speed much more safe.
Many of the areas that were governed to 8mph were very popular boardwalks, after many people were injured and an older guy was hit and died. The convention center is more nuanced, because lots of it is heavy traffic street. But there is no reason a scooter needs to go even 8mph on the boardwalk, imo. Often times people are on them in groups bombing by you, and if you're trying to just go on a walk and enjoy the beach with kids or dogs its kind of lame.
If it's being used to commute, you can go literally 60 feet inland and go as fast as you want.
Maybe I was just in an unfortunate spot, but much of my journey from my hotel to the convention center was limited to the low speed. Would require multi-block detours to get to full speed. I agree the boardwalk makes sense at 8mph (or anywhere that there's mixed pedestrian traffic), but whatever that main road is had the restricted speeds too which felt too onerous with the much higher speed traffic along side.
Also - last week Lime announced they were pulling out of SD: https://www.kpbs.org/news/2020/jan/09/no-more-lime-scooters-...