Twin 45s are way to big for A15 unless is absoulty wild. How long have you had them on the a15? Sounds like a richness problem to me. If you can here a pressure sound check all your line to the carbies and seals. Have a look on the little Brass cap on top of the carbies see if there is fuel coming out of them, you can undo the cap as they are your main fuel jets. if your having a flooding problem you can see from there, could also be the fuel bowls.

Are the carbies spitting and popping?

What size chokes are you running on the 45s?