cdo.wikipedia.org/wiki/T%C3%A0u_Hi%C4%95k

Official Okinawan historical sources distinguish Shunten's accession in 1187 from the later unification of Ryukyu/Okinawa.

• The Naha City Museum of History says: "In 1187, Shunten Dynasty has started" and separately explains that "Sho Hashi ... accomplished unification of the three powers." In its chronology, it further specifies that in 1429 Shō Hashi defeated Nanzan and "three powers ... were integrated."
• The City of Urasoe likewise states that Urasoe was the capital from 1187 to 1405, but that only after defeating Hokuzan and Nanzan did "Shō Hashi ... became the first ruler to unite the entire island of Okinawa, creating the Ryukyu Kingdom in 1429."

So 1187 marks Shunten's rise/beginning of the Shunten dynasty, not the unification of Ryukyu. The post's claim attributes the unification to the wrong ruler and the wrong date.

Ryukyuan historical references consistently give the Tenson dynasty as lasting 25 generations, not 15.

• The Naha City Museum of History describes the "Tenson-shi Dynasty (25 generations, 17802 years)."
• The Ryukyu Shimpo Okinawa dictionary likewise says the legendary first royal line "continued for 25 generations" before the 25th ruler was overthrown and Shunten took the throne in 1187.

So the post's figure of 15 does not match the standard count used in Ryukyuan historical materials.