Samsung has come a long way to clean up their user interface on their latest handsets, the Samsung Galaxy S6 and Galaxy S6 Edge, with a lighter TouchWiz experience and less bloatware according to Samsung when they officially unveiled both phones back at Mobile World Congress on March 1st, 2015. Some of this can be attributed to the company's adoption and distribution of Lollipop on both handsets, but it seems that Samsung has also drawn a little bit of inspiration from their own in-house operating system known as Tizen, which was officially launched on its very first smartphone, the Galaxy Z1.
While not all of the UI takes queues from Tizen, you can see from the comparison image below showing the contacts application from the Note 4 running on Kit Kat and the Galaxy S6 running on Lollipop, that the contacts app design bears a resemblance to the contacts app design in the Galaxy Z1. The round contact bubbles containing the caller ID photo for each contact look pretty similar, although admittedly this is the only aspect that appears to be the same within this app on both mobile platforms, but without a Tizen phone or a Galaxy S6 in hand to compare other elements there is no way to know. There are other things included in the Galaxy S6 and Galaxy S6 UI though that have already been introduced with Samsung's first Tizen handset which some people may have overlooked.
Back when Samsung unveiled the Galaxy Z1, they stated that it would include a system for implementing themes where users would be able to swap out various things to customize the look of their device, including icon packs, fonts, color schemes, and keypad designs etc., all things which are now included in both the Galaxy S6 and Galaxy S6 Edge with their new theme engine. It's possible that Samsung may have been inspired to inject other elements of the Tizen UI into the new TouchWiz UI on the Galaxy S6 as well, and so long as the result is a cleaner interface with a more enjoyable user experience, consumers likely won't care.