That's total ******** m8, I don't know a single postie that would start 15 minutes early without pay nevermind 90, why would they? Not using trolleys properly and leaving parcels would be more commonplace though.
Believe me it is rife, it is the main reason RM does not use clock-in/out machines because if used correctly, it would show far more "man hours" (i.e £££) are needed in a depot than they can hide by not paying all these early starters that work for free (because it is not authorised overtime).
They do not leave work earlier to make up for the start, everyone is expected to work until their contract finish time. They work for free early on because they want to finish at their contract finish time, rather than delivering their round until the late afternoon and claiming overtime (which RM has a reputation of not paying in full).
They have a "skilled" group of employees who put garbage (data) into a program that then churns out garbage about what a postie can do, a horrible case of "GarbageInGarbageOut." So when posties work as they are supposed to, the managers say something to the effect of "the computer says the complete day's workload {both indoors and outdoors for "round x"} is achievable," in reality there is typically 60-90mins of excessive workload even outside Xmas.