FYI here is how reducing that number helped with my clocktable updates in the order I tested each value.
*** org-element--cache-self-verify-frequency 0.01
update takes 1:18 (minutes : seconds)
*** org-element--cache-self-verify-frequency 0.005
update takes 0:48
*** org-element--cache-self-verify-frequency 0.002
update takes 0:28
*** org-element--cache-self-verify-frequency 0.001
update takes 0:19
*** org-element--cache-self-verify-frequency 0.0005
update takes 0:20
*** org-element--cache-self-verify-frequency 0.03 (default value)
update takes 3:29