There is a speedway competitor on this forum and also a crank machinist that uses the e13 series crank into a12 and also uses the ohc e15 head to make it an OHC A series.

Now this would be possible to do it the other way round.

The other thing is that the e series crank has the 40mm rod journals which are like bike engines and offer that little bit more all up.

Another method would be to keep your a15 crank use the e15 rods and offset and resize the rod journals to increase your stroke.