It depends on how the fuselage is modeled to be honest and I'm not too familiar with the A-10. The 3D Lab Print website notes the A-10 is meant for fully vase mode printing which could mean two things. If the internal geometry is fully modeled using sheets or solids, the infill won't really matter since none of the geometry prints as infill. if the geometry is modeled by cutting thin slices out of an otherwise solid piece, however, the infill could add some weight. It also depends on how much volume of the geometry the infill would take up. In some designs, half the volume of the plane is infill space while in others it's not much of the volume at all.
My suggestion would be to slice it with the infill and without in vase mode (as intended) and compare the weights. That should give you an idea of how much heavier the plane will get.
In terms of using PLA vs. LW-PLA, I'd probably suggest going with LW-PLA if at all possible. Normal PLA works great for 3D printed planes if they are designed for it but is roughly twice the density of LW-PLA. You will be adding at least 1 kg to the weight of the plane. I suspect the plane would still be light enough to fly with a sufficiently strong power system if printed in normal PLA, but I wouldn't necessarily trust the structure to hold up to the increase weight. PLA may be stronger, but it's worse at absorbing shocks like landing. Especially with the extra 15% infill, you could have a quite heavy plane.
The manual should give a better idea if PLA is acceptable or if LW PLA is truly necessary.
