Screen size may be small, but you have the power to run the programs.
I have a 2012 i5 13″ mac and a 2011 i7 15″ mac. They can both run the programs you speek of but i have switched to Affinity photo and Design (licence covers up to 5 computers using the same account and free updates) I still have LR though. The 13″ is just easier to carry back and fourth.
If you can get used to the small screen size on a 13″ than go ahead but you will most likley enjoy the extra inches of a 15″
A lot of people at college and uni manage fine with 13″ 8)