In this version, I added what is known as Object Pooling. The truth is, I had no idea that instantiating and deleting objects consumed such a large amount of resources. It wasn't until I started researching optimization that I realized I had to stop doing it. In this version, I applied it to the shots of the 4 ships that are currently available, and the performance increased much more than I would have expected.

I'm new to this, but if anyone knows more optimization techniques for a shoot 'em up, I would greatly appreciate it.