How I can consolidate multiple projects by keeping the same namespace and move them into Domain Driven Design project? We are not a software shop and our code is not an API with no intention of being extended. Plus we have like 150 projects in our solution code base makes comprehension hard for developers and IDE performance really slow. we have implementation projects, and then "domain projects" w/ Interfaces, POCO models and enums and in most cases we only have one implementation projects.
Start by creating a folder within the solution by separating projects by features or departments and one folder for cross-cutting or shared projects as you prefer.
After that, within each folder you created for each feature you can add other subfolders to Data Access, Domain Model, Application and UI.
This already will be a good start to application of DDD.
Probably after that you should start discover best opportunities to increase the quality of your code.