Ways to reproduce:
-Get to a high ground, look down to the ground with high view object distance. Check if frame rate dropped drastically.
*Update*
After some more testing I came to the conclusion of mod conflicts. But unable to confirm.
Mod List: CBA_A3, All in Arma, RHS (Both Russian and US) and ACE3, all are up to date version.
Despite the fact that I suspect it was RHS and ACE3 were the cause of the issue. But due to the high popularity of both RHS and ACE3, such glaring issue should already been reported. So that just makes whole situation even more confusing.