Hello @epiko, while powering up 1.5 HIVE during the Power Up Day will still contribute to your Hive Power, it won't be enough to earn you a badge, as the minimum requirement for the smallest power-bee badge is 10 HIVE.

Considering this, it might be better for you to wait until next month and power up with 10 HP or more to be eligible for a badge and potentially receive other benefits from participating in the Hive Power Up Day event.