Q.Spring care of orange tree
I have an orange tree that lives in a non heated sunroom. This winter has been a very harsh and prolonged one. All the leaves are wilted and dried up and the few fruit that developed over last year are discolored and mushy. Should I trim the branches back aggressively or just allow the dead leaves to drop?

I does appear that your tree has been exposed to below freezing temperatures. Your tree would not be able to tolerate temps below 25 degrees.
It may not have survived the cold. I do always give plants a chance, so yes, go ahead and trim it back. If you have new growth the root system may still be alive.
Here is a link to orange tree care.
https://www.gardeningknowhow.com/edible/fruits/oranges/orange-tree-container-care.htm