There are a few things to check:
If you play in a new editor window or stand-alone, check the Viewport options before running and make sure that Realtime is unchecked, otherwise (it seems) the editor keeps updating in the background, which effectively cuts the framerate nearly in half.
Also check your Scalability settings: Effects and Post Processing seem to be the most demanding on my system, and dropping them to high or medium typically makes a huge difference. Resolution Scale can be dropped below 100 (try 75) if you are getting a low framerate when running tests in fullscreen.
Finally, make sure you don’t have any Blueprint event graphs or other separate editor windows open while playing, because they too seem to be chewing up cycles even when they are technically supposed to be idling in the background.
I do most of my prototyping on an i7 laptop with a very modest GTX 460M GPU and a measly 6 GB RAM, but using the tweaks above, it’s typically possible to get a usable framerate in the +30’s on somewhat simple test maps.