No, it was always around 0.1%. The earlier figures were known from the start to be wrong by people in public health because early attempts to estimate IFR are always wrong (always high). They don't get reports about mild cases until they start looking for them.

Even people like Neil Ferguson gave up claiming it was 1% early. No idea where you're getting 3%-15% from.

The IFR fell "post vaccine" because of a mix of how vaccination status was defined and because Delta soon mutated into Omicron, which was just a normal cold virus and not deadly at all.