Major bug in Minecraft 1.13 to 1.14.4

 

The 1.15.1 version of the game works, but it's very slow (1 to 4 fps, with a lot of freeze) on old hardware (look at the below environment section).

Other major bug of Minecraft launcher :

Hello, I found a very ugly bug on Minecraft Launcher 1.6.93 and Minecraft launcher 2.1 that makes the loading of the game freeze at 50 % on old hardware.

The bug doesn't appear on recent hardware.

Java arguments used :
-Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn768M

Fatal error on launcher log :

[13:06:23 FATAL]: Fatal error launching game. Report this to http://bugs.mojang.com please!
java.io.FileNotFoundException: File 'C:\Users\FellFromTheSky\AppData\Roaming\.minecraft\assets\indexes\1.15.json' does not exist
at org.apache.commons.io.FileUtils.openInputStream(FileUtils.java:299) ~[launcher.jar:1.6.93]
at org.apache.commons.io.FileUtils.readFileToString(FileUtils.java:1711) ~[launcher.jar:1.6.93]
at net.minecraft.launcher.Launcher.cleanupOrphanedAssets(Launcher.java:298) ~[launcher.jar:1.6.93]
at net.minecraft.launcher.Launcher.performCleanups(Launcher.java:540) ~[launcher.jar:1.6.93]
at net.minecraft.launcher.game.MinecraftGameRunner.launchGame(MinecraftGameRunner.java:209) ~[launcher.jar:1.6.93]
at com.mojang.launcher.game.runner.AbstractGameRunner.onDownloadJobFinished(AbstractGameRunner.java:186) [launcher.jar:1.6.93]
at com.mojang.launcher.updater.download.DownloadJob.popAndDownload(DownloadJob.java:122) [launcher.jar:1.6.93]
at com.mojang.launcher.updater.download.DownloadJob.access$000(DownloadJob.java:12) [launcher.jar:1.6.93]
at com.mojang.launcher.updater.download.DownloadJob$1.run(DownloadJob.java:86) [launcher.jar:1.6.93]
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.8.0_231]
at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.8.0_231]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [?:1.8.0_231]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [?:1.8.0_231]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_231]