This movie is not your typical thriller or comedy. This movie intertwines both genres into a story that is an amalgamation of Fargo, rear window and the Road to Bali. Of course murder isn't a laughing matter, but Suburbicon flips your moral compass so you can laugh at death.
If you are wanting a funny movie, this ain't it. If you are looking for a serious crime thriller, this ain't it. Are you looking for a movie that blurs the lines between murder and cracking a joke, while also calling into question the white flight from the cities in the 1950s, than this is your movie. Throw in a little Red Scare hysteria and this is serious critique on the USA in the 1950s.
The movie may be slow, but that is the point. Enjoy the movie for what it is, laugh when it is funny and cringe when it is trying to make you cringe.