In general... It depends. In your specific case I would lean towards putting in extra effort on work projects. You know the domain already and probably have a

In general... It depends. In your specific case I would lean towards putting in extra effort on work projects. You know the domain already and probably have a lot of interesting contributions to make. But a word of advice: don't tell your manager etc that you are working more hours lest it become an expectation. With 15 years experience nobody is going to pay you more for having a basic side project.