Mark 15 once again is going to be largely a repeat of the issues in Matthew 27. Looking through the notes, I see two issues not covered yet, one of which I have an answer for, and one of which I don't.
"Did Jesus drink from the cross?" It may be worth noting that in the two verses shown here, there are two different substances being offered to Jesus to drink. At the Last Supper, Jesus said that he wouldn't drink wine again until in his kingdom, so when they offered him wine, he refused. That doesn't mean he couldn't take anything at all to drink, and so I figure at a separate time they offered him vinegar and he took it.
"When (at what hour) was Jesus crucified?" There does seem to be a true contradiction here, and while I have heard there were different methods of reckoning time in the first century I don't know that any of them make this work out. Mark seems pretty clear that it was the "third hour" which means mid-morning, but the other Gospels all make it sound like an afternoon event.
Oh, and I guess I could make a response to the note on verse 33. If the darkness spoken of (which was not called "complete" darkness) was something like a solar eclipse, that would be noteworthy, but since it doesn't say, it may have simply been a sudden heavy cloud cover, which would hardly be historically notable.