2.5ghz vs 2.8ghz

Hello to the community! Im a UI Designer and work at home with an iMac mid 2010 and id like to upgrade and be portable. Im having 2 offers at a greek forum which are both 1 year used and the only differences are: 1 - MBP Mid-2015 15" MJLT2LL, 2.5 GHz, 512GB SSD, 120 cycles battery. price: 1650...