Hello, I have just purchased my first apple macbook pro 2015 retina 8 gigs of ram model. The purchase was made about 4 days ago so I am still within the return period. The day after I made my purchase I went back to the apple store to get an exchange processed since there was terrible UI lag in Yosemite. The replacement model had relatively less UI lag but still noticeable so I brought it home anyway hoping that an OS update would fix these issues. So far the lag persists through the developer previews and even the new beta for El Capitan. I have searched through the internet and it seems quite a few people are having issues with UI lag, but I am not sure about the percentage. Would you guys recommend I try to exchange another model or is that a futile exercise since most machines are impacted? I will probably end up returning this machine if there isn't an improvement. Possibly opting for a Dell XPS since Windows 10 is a huge improvement over 8. The lag is noticeable when resizing windows and even launching apps like Safari, it isn't horrible but still ruins an otherwise pleasant experience.