If you want to improve your project management skills, and especially if you don't have a lot of experience with working in environments with formal project management across a departments or sizeable teams, then sure, formal training could be useful.
You don't necessarily have to adopt all of the specific methods and terminologies etc of a specific system benefit from learning that system. Any project management system has to confront certain challenges inherent to complex projects and provide tools to deal with them, so even if those particular tools don't work for your situation, the perspective and ways of systematically breaking down a project into parts that can be effectively dealt with can be very useful, especially if you haven't yet had much opportunity to work in formally managed projects, or visibility into the way that projects you've contributed to are managed at the top level. As a regular project team of one, you're already handling all of the complexities of a given project, but you can't immediately take the way you're managing a project as a solo developer and apply that to a big project with a bunch of people with expertise in and responsibility for wildly different disciplines or parts of the project. Bigger projects require more coordination and better communication between contributors, and project management is intended to help facilitate that.
I've no direct experience with PRINCE2, but the wikipedia article doesn't raise any particular alarm bells, and even if you find that its solutions don't fit your projects' needs they can still be useful to clarify your thinking about how to manage projects and could be jumping off points to find a more suitable system that works better in your environment, or develop your own management techniques. Whether it's worth sitting through a four day course is a harder question to answer.