Sure you can develop for older platforms.
- Be sure to package for production, not development
- Check if there’s any code that’s eating your CPU, especially tick events
- Be gentle on rendering, use small texture sizes, don’t overuse dynamic lights, etc
There can be many reasons your game is running with low FPS, luckily there are hundreds of performance debugging possibilities and tutorials, check on Google and YouTube. The official one: Performance and Profiling | Unreal Engine Documentation