It seems the requirement has been relaxed a bit:

"Puerto Rico Senate Bill 864 increases the potential impact of Act 22 by expanding who qualifies for the tax break. Prior to this legislation, Act 22 was only applicable to new migrants to Puerto Rico who had not been residents for the 15 year period before the Act went into effect in January 2012. That period has now been reduced from 15 to 6 years."

https://www.forbes.com/sites/janetnovack/2015/01/27/puerto-r...