If you're describing hop flavor, the 1oz of Williamette at 15 min will give you that.
If you're describing rather bitter, maybe a bit of a harsh bitterness, the beer is likely green and will mellow some, but it will always have a solid hop bitterness to it. Galenas usually run 13% AA and clusters 7-9%AA.......given that you'll have a stout with a moderate-high hop bitterness.
I assume you're doing a partial boil too, otherwise that many bittering hops in a stout would be extremely bitter........
With stouts, porters, etc. I find it takes a good 2 months to mellow to the point where I think they're really getting good. FWIW
Be patient, you're beer will be ok.