If its any reassurance I did not find the side effects all that strong going from 10 to 20 mg so you may be ok in going from 10 to 15mg. The changes in our anxiety obviously get affected by events around us so you may have had more triggers around on the bad days. Sometimes a dose that supports us on a good day is not enough to hold us up on a bad day.

Also, are you taking the medication at the same time each day and at the same time relative to meals. That should help to keep your internal dosing more consistent.