Crashing and 100% CPU in 18w21a

When I play in the snapshot, on ultra minimal settings (fast graphics, 2 chunks etc.) It uses 40% or more of my CPU, Using low quality settings (8 chunks, smooth lightning minimal, fast graphics) It uses 100 % CPU and crashes after a minute or 2. Last snapshot it used max 60 % CPU and in 1.12.2 40%. RAM uses is also messed up because it uses 2,5 GB of ram instead of 1,5 in 1.12.2. Please fix because MC is unplayable.