i really dont think it will be a problem, delta is an airline but also a common word.
When we chose this name we were certain that we won't have any troubles.
Respectfully, unless you have a letter from Delta legal, I find it very hard to believe that they wouldn't bring action. Even assuming, arguendo, that your right, it's a waste of investor dollars to prove that in court. This would be a red flag for me, were I a potential investor.