So... there's a separate 15 year gift box that is probably what you are thinking about (https://www.lotro.com/news/lotro-15th-anniversary):
15 Year Giftbox!
Additionally, we will once again have a 15-Year Giftbox available in-game that can be claimed by logging in between April 20th, 2022 after 10:00 AM Eastern (-4 GMT) until 3:00 AM Eastern (-4 GMT) on April 1st, 2023.
This gift will be delivered to any player that logs in and previously claimed the 14-Year Giftbox.
It includes:
Free Players (non-PvMP):
Soaring Pinwheel Fireworks
Fifteen-Year Portrait Frame
Title: Clear as Crystal
Creepside Players (PvMP):
Flaming Pinwheel Fireworks
Fifteen-Year Portrait Frame
+5% Attack Damage x5
Title: Crystal Shatterer