Perhaps it's too early to start asking about 1.15.1 rending changes. But I'm going to anyway.
I've created a test mod with exactly one block. Said block is merely an instance of the vanilla GlassBlock, using the vanilla Block.Properties (copied from Blocks):
Block b = new GlassBlock( Block.Properties.create( Material.GLASS ).hardnessAndResistance( 0.3F ).sound( SoundType.GLASS ).func_226896_b_() );
b.setRegistryName( "testglass" );
event.getRegistry().register( b );