Infanta D.Maria Ana of Bragança was 15 when she married Crown Prince George of Saxony.
Her sister Infanta D.Antónia was 16 when she married Pr.Leopold of Hohenzollern-Sigmaringen.
Infanta D.Maria Francisca was 16 when she married her uncle D.Carlos of Spain
Infanta D.Maria Ana Victoria was also 16 when she married Infante D.Gabriel of Spain.
If you mean just betrothal w/o wedding, Infanta Mariana Victoria of Spain was engaged to Louis XV in 1721 when she was 3 and he was 11.
The marriage was later broken.
In 1722, Mariana's brother Luis, Prince of Asturias, aged 15. married Louise Elisabeth d'Orléans aged 12.