Brandon, absolutely yes. A 15rd magazine handgun is legal for transfer in IL. You and yours stay safe Sir!

yes as long as it is not banned for another reason Illinois does not have a mag capacity ban on handguns it only applies to long guns "Box-type detachable magazines with a capacity over 10 rounds are prohibited only for long-guns" as far as handguns Prohibited are semiautomatic pistols that have a detachable magazine AND two or more of the following: Any feature capable of functioning as a protruding grip that can be held by the non-trigger hand A folding, telescoping or thumbhole stock Barrel shroud Muzzle brake / muzzle compensator Capacity to accept a detachable magazine outside the pistol grip budsgunshop.com/feeds/state_reg/illinois_restrictions.pdf

Yes, they will ship whatever comes with the gun. You just can't buy a mag over 10 rounds on line and have it shipped home in Illinois. You can also go to your local gun range and buy what ever off the shelf. Just can't order on line more than 10 rounds. I did this last week, buds shipped me a 17 round H&K then went to range to try it out and bought another off the shelf.