Compared to 1.14.4 the newest snapshots perform very, very poor on my system. Framerate is zero most of the time (sometimes little bursts happen for a short time).

Test: I created new worlds (both seed: TEST) in 1.14.4 and 19w42a respectively. Then waited some time for world creation, before creating debug profiles/reports and making screenshots.

Result: While 1.14.4 after some lagging is playable (though not enjoyable, 'cause still too laggy), the 19w42a snapshot is a slow dia show and not playable at all.