One of the ongoing problems with Samsung devices has been the lag in touchwiz. The Galaxy S6 and Note 5 finally provided us with enough CPU power and Ram to do a decent job at masking this lag. Still there are parts of touchwiz that lag due to the hundreds of processes running in the background mostly having to do with bloat that are not necessary.
Some of the lag has been demoed in a series of videos. I have had my Note 5 since day one and can say that I have also noticed some lag. Also switching back to the Note 5 from the Nexus 6P several processes are just slower.