Unless you live very near to Newcastle station and your course and placements are very near York station, I suspect your journey would be a lot more than 90 minutes in reality.
The train journey itself is 60 minutes. 15 minutes at either end is not a lot at all; you could use 5 minutes just walking to your platform from the station entrance.
Also, the time that you would need to travel (rush hour) means that you may need to double (or triple) the time it takes to travel to and from the stations.
To give you an idea: I commute to a major Northern city from my home 20 miles away. The train journey itself is about 45 minutes. Ideally, the entire journey, door to door, looks on paper as though it should take 1 hour and 15 minutes.
However, in reality, the entire journey takes me 1 hour and 45 minutes. Traveling at rush hour means it takes me twice as long to get to the station from my home, and the walk from the station to my office takes longer than it should.
Then other extra minutes are spent waiting for the train, moving through the stations, waiting to filter onto stairs or escalators, waiting to go through gates, navigating past the throng of people in the bottleneck outside the station, and then getting into my office building ... if you need to be sat in a seat at a certain time on the dot, it can get really stressful.
And the whole thing is knackering. I couldn't do it five days a week. When I am tired at the end of the week, after three days commuting, that return home journey seems to take forever.
If I were you, I would trial the journey at the time you would be traveling. And do check out train fares ... they have become very expensive.