To reduce the size of your newly edited video, you should try adjusting the export settings in Chimp Clip. Make sure to lower the resolution, bitrate, and choose a more efficient codec like H.264. This should help decrease the file size significantly. The reason your 15-minute video is still so large is likely because it's being exported with the same high settings as your original 200-minute video.

I read an article about iMovie for Windows and some alternatives like Movavi Video Editor. Movavi is praised for its user-friendly interface and efficient export settings, which can help reduce file sizes without compromising quality. Considering your issue, Movavi might be a good alternative to Chimp Clip. It's affordable and could help you manage the size of your edited videos better. You might want to look into iMovie for Windows as a reference for user-friendly editing software.