The bug

Using the latest snapshot for 1.14, particles, even in smaller amounts, create an unusually large amount of lag which is not the case in older versions. Note that this is a separate bug and is not a duplicate of MC-124170.

How to reproduce

1. Get yourself a Command Block with this command:
   /give @p command_block
2. Place the Command Block and set it to Repeat mode and Always Active. Set this command on the Command Block:
   /particle firework ~ ~1 ~ 0.01 0.01 0.01 0.01 10 force
3. Repeat steps 1-2 until it reaches at least four Command Blocks.
   → Notice that it eventually causes an extremely large amount of lag. What makes it significant is that it does not affect older versions (such as 1.13).