Yes, the NF-A15 PWM bundled with our heatsinks is specified to run at 1500rpm (see cooler specifications for details) and the retail model is specified to run at 1200rpm (see fan specifications for details).
On dual-tower coolers such as the NH-D15S, we recommend running the 1500rpm version in the centre and the 1200rpm version on the front. On single-tower coolers such as the NH-U14S, we recommend running the 1500rpm version on the front and the 1200rpm version on the back of the cooler.
The NA-YC1 supplied with the retail fan can be used in order to control both fans via one PWM fan header. In this case, both fans will scale individually according to the PWM duty cycle supplied by the motherboard, e.g. they will run at ~1500/1200 respectively at 100% duty cycle, ~750/600rpm at 50% duty cycle, etc. Both at 100% and lower speeds, the speed difference between the fans reduces resonance phenomena and thus helps to achieve the best balance of performance and noise.