It is crucial that you get this time of 0855 out of your head, the vital time is 0815! That is when check in will close, on the dot. Miss that and you start from scratch with a new ticket, and walk up prices can be high. Easyjet are great but you have to be on time, and that is the time on their computer and there is no flexibility.
Personally I would never schedule two separate flights with less than an hour between them but you may well get lucky. Basically you have left no room for any problems, so if there are no problems you will be fine.