My iPhone 6s also showing the same battery drain issue after updating to 14.2. Now need to be charged full (which takes now much longer) twice a day to get through the day even without heavy usage. My partner’s iPhone 7 also showing the same problem but a little less severe.
Even though it has been reported by a lot Apple users, I see no response from their part. This is really frustrating as a longtime iPhone user. I don’t intend to upgrade to any new OS until unless it guaranties the omission of the battery drain issue.