i-Size regulations require rear-facing until at least 15 months, but the safety case for staying rear-facing goes well beyond that minimum. A rear-facing seat spreads crash force across the back and shoulders rather than the neck, which matters most while a toddler’s neck and spine are still developing.
This is why a growing number of "extended rear-facing" seats now support rear-facing travel up to around 4 years old, rather than switching to forward-facing at 15 months as soon as it becomes legally permitted.
If you’re deciding between a seat that switches early and one that stays rear-facing longer, and your budget allows it, extended rear-facing capability is one of the higher-value safety features to prioritise — more so than most other spec differences between seats.