So after searching through issues I couldn't find a similar one posted that wasn't tagged resolved and this certainly isnt

Upon loading any world created in 1.14 there are huge fps losses in previously loaded chunk, any command blocks in the world cannot be opened or edited and neither can command blocks that have been placed down after loading the world.

If a world is created from. New in 1.15 command blocks can be placed, edited but only until their type (repeating, chain etc) is changed at which point they become 'locked' and cannot be opened or edited again.

When using a resource pack fps drops to as low as 5. Confirmed through a friend this affects any world created in 1.14 and opened in 1.15 with a texture pack enabled in our case bd craft. If u drop the quality to 32 it alleviates some of the issue but doesn't affect the command block problem

I use hundreds of command blocks and this update has effectively rendered the game unplayable for us