Issues with fast charging can be because of 3 reason. 1. Faulty data cable. 2. Faulty charging adaptor. 3. Faulty charging port of your phone.
Try changing the first and second items. If the issue is not solved take the phone to a service centre for replacing the charging port.
Slow phone can be fixed by, 1. Cleaning the cache and freeing up storage by deleting unnecessary apps. 2. Try taking a backup and reset. In worst cases slow phone can be because of hardware issues also. Any way try fixing the charging issue first. Some times a damaged charging port can slow down the device as now a day's charging port is an interface for lot of other accessories like HDMI, audio accessories, OTG, etc.. which directly intearfear with phones performance.
