Framerate Issues
After the 1.15 update, performance became very poor. My framerate halved, and I had to go down from 32 chunks to 20 for it to remain in the 50s.
The world I had been playing in did have a significant number of entities, but opening a new world in 1.15.1 showed continued performance problems.
I tried switching the amount of allocated RAM from 12GB to 6 but saw no improvement or change in the framerate.
I've messed with framerate settings, and that hasn't affected performance.
My system:
Alienware Aurora R7
Intel Core i7 8700
32GB DDR4 2666MHz RAM
GTX 1080 8GB
Incorrect Scaling
If I allow the game to detect the resolution in the launcher, scaling goes up by ~200%, and GUI scale is also double its proper size. The splash text is pixellated while this happens. If I switch back to the desktop, I can see that it's impacting Windows 10 as well. My desktop will have huge icons for a couple of seconds until Windows changes the scaling back to normal.
There is a fix for this. If I set the resolution in the launcher to my monitor's resolution, the game will properly scale to my monitor's resolution.
1440p@60Hz
Linked issues
Comments


Also, check what version of java you are using, if you're using the 32-bit version that is probably the reason why you have so poor performance if you are using 64-bit Java Version 8 Update 231, try using Java Version 8 Update 51 that is Minecraft set by default to run. If you don't know how to see what version of java are you using just press F3 and on top right corner you will see version.

Hello!
I've tried VSync on and off and changing max framerate to multiple different levels, but to no avail.
I'm running Java Version 8 Update 51 64 bit.
I did notice a performance increase after I unplugged my second monitor (which was cloning my display,) but performance is still significantly reduced from 1.14.4.
The largest factor it seems is the chunk loading. I'm aware that they changed this to be much smoother, and I wonder if the change had a significant performance hit.

Word on the chunk loading- loading a 1.15 world (from a ~400Mb read SSD no less) has seen a MASSIVE performance drop.
I wonder if there's just been a big problem introduced in Minecraft's ability to load stuff. MC-166846 has me nearly pulling my hair out when I'm trying to texture.

Maybe that's part of my problem. For whatever reason, Alienware opted for a hard drive with Optane instead of a hard drive and an ssd.
I used the "optimize button," but it had no impact on performance (or bee spawning, for that matter.)
Did you try turning on Vsync and set framerate limit to unlimited.