I'm a PM on a large multi-year project with a sizable backlog of work implementing Scrum in 4 week release cycles. I hold weekly backlog grooming sessions with the project team and key business owners to review the user stories in the backlog, break down larger user stories (epics) into smaller ones that the project team can begin implementing in the sprint and size these smaller user stories using story points.
The use of story points associated to a user story is a fairly new concept to the team and has only been implemented in the past 6 months of the project (that started 1.5 years ago). So, the entire backlog is not sized in story points.
My goal initially was to introduce the team to story points and to establish a regular meeting for the team to size user stories in the backlog so that they get used to it and thereby become more efficient (read faster) at sizing. However, the team has plateaued in terms of the speed at which user stories are sized and at the current rate I estimate it would take upwards to another year to size the entire backlog.
Is this a good approach to sizing an entire backlog (that is very large) with the project team? How can I move forward with this in a manner that will speed up the process? If not a good idea, what is the better approach to this process?