The 15mph speed limits added in https://www.openstreetmap.org/changeset/117307095 look questionable.  

The state law that allows special school zone speed limits only applies within 500ft of schools, and the school zone 15mph signs I see around here in Mapillary say "...when children are present".  The state only very recently changed the law to allow cities to set speed limits below 25mph and I haven't heard of SF changing any streets to less than 20mph yet. (see https://walksf.org/2022/01/19/speed-limits-now-20mph-on-seven-streets-a-key-step-to-slowourstreets/ )