have to rebuild main project for changes in other projects

Question

I am working on web application in VS 2015. In a solution, I have two projects one is for Web APIs and other is for UI. I added reference of API project in UI project. When I change something in API project I need to rebuild UI project too which takes too much time. Is there any other way that instead of rebuilding UI project I can just replace dll or pdb files of API project.