Is there an issue with the boards not being updated? Certainly. However, there's nothing legally that Delta is required to give, and getting you to your destination and giving a $150 voucher seems adequate, especially if the delay was only a couple of hours.
Cutting it that close, even assuming it was a full 15 minutes before departure and not 13-14 minutes rounded up, is still a bad idea. Especially with a tight connection, check the gate area first and then see if there's time to grab a snack or something. Things change and always aren't communicated perfectly, and cutting it to the last minute will cause issues. If a line is longer than expected, a moving walkway is down, or something isn't communicated on the boards, you'll hit a snag once in a while.
Frankly, you're almost certainly not going to get any cash compensation from Delta. You might be able to push and get a few more Delta miles or get them to give miles instead of a voucher, but if you've sworn off Delta and a voucher/points are worthless there's not going to be anything that you'll get that's worth spending your time arguing for with Delta.