Slow highlight with fuzzy search

As the database got bigger (150 000 records) I’ve noticed strange
behaviour of highlight() function. When using fuzzy match ~ it takes
even 15 seconds to wait for the highlight function to finish its job.
While without fuzzy match it takes only a fraction of a second. Note
that when not using higlight both fuzzy and normal searches are fast
(less than 1 second).
No database queries are performed during highlight (at least logs show