Macbook pro late 2011 can support 16GB 1600Mhz RAM
Apple MacBook Pro "Core i7" 2.4 15" Late 2011

Standard RAM:   4 GB    Maximum RAM:    16 GB*

Details:    4 GB of RAM is installed as two 2 GB modules, no slots free.

*Apple officially supports a maximum of 8 GB of RAM, but third-parties have determined that this model actually is capable of using up to 16 GB of RAM with two 8 GB memory modules.

Speed:  1333 MHz

Details:    Supports 1333 MHz PC3-10600 DDR3 SDRAM.

So buying 1600Mhz wont do much, just waist of money.

Shop here: http://eshop.macsales.com/shop/memory/Apple_MacBook_MacBook_Pro/Upgrade/DDR3_1333MHz_SDRAM

Learn how to here (video): http://www.everymac.com/systems/apple/macbook_pro/macbook-pro-unibody-faq/macbook-pro-13-15-17-mid-2009-how-to-upgrade-ram-memory.html