Although an 'event', items were added to the 1st Floor on the 17th, and more were added on the 18th, 19th, and 20th. Teru teru bozu are amulets that are supposed to bring good weather and prevent a rainy day.
The strawberry umbrella was a surprise update on the 23rd of June. The 15 in 915 is a pun. 1 (ichi in Japanese) and 5 (go in Japanese) give ichigo, Japanese for strawberry.