Because SketchUp 2015 reached its "End of Support" on January 31, 2018, it is no longer officially available for download or technical support. Trimble recommends the following alternatives: SketchUp Free (Web)
Given the serious risks associated with the "portable" version of SketchUp Pro 2015, it is highly recommended to use legitimate software. Here are the best paths forward for different types of users: Because SketchUp 2015 reached its "End of Support"