In the past we have discussed punctuation problems (here on James 4:5). Yesterday evening I was reading Chrys Caragounis on Romans 5:15-16 and he came up with a simple and quite brilliant suggestion for which he needed only 6 pages including footnotes (brevity being a sign of strength). He suggest reading the phrases
αλλ ουχ ως το παραπτωμα, ουτως και το χαρισμα (v15)
και ουχ ως δι ενος αμαρτησαντος το δωρημα (v16)
as rhetorical questions expecting a resounding Yes!
The translation of v15 would be something like 'But is it not as the trespass, so also the gift?' Or 'The gifts is as the trespass, isn't it?' Or, in Caragounis' words 'But does not the free gift operate just like the trespass did?'
This results in a great flow and explains how Paul can use the concluding αρα ουν in verse 18. Taken in this way, the basic mode of the whole passage remains that of comparison. And the only thing we have to change in our Greek edition is the punctuation.
(Chrys C. Caragounis, "Romans 5.15-16 in the Context of 5.12-21: Contrast or Comparison?" NTS 31 , 142-48)