There is no such thing as an offline installer any more. The setup downloads and installs the latest available components online.
The only possibility is to ask support if they have a cd install they could make up and send you they used to be able to do that 3 years ago but now I am unsure. They did it for a user on dialup but it took a lot of calls to get it as it is not usually offerred if possible now.. I do not suppose you are allowed to connect your PC to the schools network that probably would be a no no.
Customer service can send you a CD install but it will be the 2014 version and will try to upgrade to 2015 when it is fully released which is not what you want..
If you want to try call Customer service and request it.