Well for me and my Oculus Q2 this is a Apache problem. I only experience massive fps drop after 10-14min with the Apache installed. I dont even need to be in it.. ones installed the drop happens in all modules after a short period of time.
I cleaned my system from DCS and did a complete install of the game. Did not install the Apache this time, and now the problem is gone!! Back to experience a solid 40fps as I normal do after 3 hrs of flying time.
So for me, there is something happening ones im installing the Apache.