I am so sorry you are dealing with this side effect of the medication. If you are on day 15, you may have reached the erosion phase and the cream may have done all it can do. This is typically when the skin becomes extremely irritated, begins to seep clear fluid, and scab over. If that is the case, you are likely ready to start the healing phase.
I suggest you check in with your prescribing physician before you apply antiseptic or any other creams to the area. I have always been told not to use anything on the treated area but water during treatment.
Can you send pics to your doctor or schedule a telehealth visit?
Please let us know what you find out. I am including some articles that may help in the next few days.
https://skincancer.net/life-with-skin-cancer/efudex-side-effects-tips
https://skincancer.net/life-with-skin-cancer/efudex-erosion-stage
https://skincancer.net/life-with-skin-cancer/efudex-side-effects
Sending you lots of healing thoughts!
April, SkinCancer.net, Moderator