Wow! That's a whole lotta hops.. 15oz for 5 gallons!
Not sure how much malt backbone you need for that kind of hopping, but I had a few thoughts on your grain bill.
I think the Victory & C-120 are not really needed. You already have the maris otter base grain plus some munich to give it toasty, malty goodness. I'd up the chocolate malt to at least 1/2# ... maybe a bit more... No more than 1# on the outside.
Hope it turns out great!