advise whether to go to skellige without finishing in nograd? (The Witcher 3: Wild Hunt)

In general, in short, the meaning is this, I'm 17 lvl. TM has sent her sorceresses. The whole map has been cleared, except for a few monsters of 20+ lvl and orders (there are still 8 orders left from 12 to 25+).
I already thought right now the plot will reach the end and go to Skellige. But new quests are constantly appearing with Roche, with Philippa, with Radovid. Meanwhile, on Skellige, quests turn gray.

So I'm racking my brains to drop everything here and go there, or don't care to finish it here? But then I'll wafer a bunch of experience from those quests.