As of Today July 17, 2019 i see that the particle lag is still here because I went into the ocean then put a bunch of soul sand in this version.Then, go to 1.14.3 and do same process, and compare both version. I  view that, I will lag way more in this pre release 6 than on 1.14.3 and I see that this is a performance issue.

THe first  picture is on the 1.14.4 pre realase 6

and the second picture is from 1.14.3

 I wish know how to record minecraft to make more sense