I'm not sure if it's lighter but after using the Now Launcher for a long time I switched to Nova Launcher Prime about a year ago on my Nexus 6P and it's been fantastic.
It has some great additional features, is well maintained and updated, and I've never experienced any crashed or UI stutters/lag due to Nova. Nova has a free version with almost all the same features as the paid version, and no ads, so you can test it out.
+1 for Nova here too - used it for years on a variety of phones, and I've not found another launcher which works as well with such a good feature set; there are lots of nice touches in there and the author seems to keep it up to date with new UI developments (such as the recent update which has some pixel features added). Well worth the small extra for the full version to help support it.
-at the moment it is not possible to integrate with Google Now the way the Now launcher does. Although it looks like this is officially going to change (and one of the motivations behind this move)
-tastes in launchers vary widely from one person to the others. I have quickly uninstalled pretty much all of the launchers I have tried since they all tend to give bazillions of options instead of focusing on good defaults.
It has some great additional features, is well maintained and updated, and I've never experienced any crashed or UI stutters/lag due to Nova. Nova has a free version with almost all the same features as the paid version, and no ads, so you can test it out.