Castalan with Eagle Mark 15 is in Hougarts book of Mexican hallmarks. The only thing we can say for sure is that the hallmark identifies the piece as being produced before 1980, when the new Number Letter system was introduced in Mexico. Having said that the eagle shape on Castelan is identified as being used between 1955 and 1980. I would venture to guess that the bracelet is far older than the charms. Do any of the charms have marks on them? Just another thing to mention regarding Mexican Sterling. I have repeatedly run across what looked like Native American work, only to find the Mexican Hallmarks. Some of them you could not tell the difference without seeing the hallmark. I have posted before on this topic.