What are these eyelets for on my 2015 Diverge?
The smaller hole is for  Specialized's proprietary "plug and play" fenders, while the larger is for a rear rack.  The larger hole can also be used as an alternate mounting point for other types of fenders. For a rear rack on the carbon frame Diverge, it is intended you use the Specialized Rear Rack Seat Collar (second picture), which combines a seat collar and mounting eyelets for a rear rack.