I have tried running your save with all your mods. I'm not seeing any dip on my pc.
Has it always been like that? Has this issue pop up recently? The only thing that run every 10 minutes is the enemy level up check. But nothing has changed to that part of the code for a very long time.
Other parts run more frequent than 5 minutes. All my calculations are done in small set. I don't see how any thing can cause 10 to 15 seconds of FPS drop. When the FPS drops, what are the stats do you see in "show-time" debug?
What if you just run only with my mods? Does it still cause the performance drop?
Are you in my discord? We can chat there. I think this may be an isolated issue.