I was able to brute-force it and get my stars for Day 11 by only searching for grids with sizes between 3-30. Mine turned out to be 16 in size. This would run in some 120 seconds 
Learned about summed area table algorithm in here, watched James’s stream (
) and now part 2 runs in about 10 seconds for sizes 1-300 
My solution is here.
