Replacing the whole lot - chain and both sprockets. Thinking of 16/44 or 16/45 combination as advised by AF1.
"If you are replacing all three, chain & both sprockets, keep the ratio the same but go with the larger front sprocket. He said a larger front sprocket is easier on the chain and the only reason many do the 15T on the front as a modification is that the OEM chain is not long enough to go 16-44."
15-41 (ratio 2.733, what I had) is almost an exact match to 16-44 (ratio 2.75)
15-42 (ratio 2.8) is almost an exact match to 16-45 (ratio 2.8125)
Stock is 16-40 (ratio 2.5)