From comments I’ve read 25fps isn’t bad in the scenario you describe - are you getting a smooth performance, which would indicate your CPU is coping?
Best tip is to set up the performance monitor in Developer mode and see if you are CPU or GPU limited. You can then decide if you need a CPU upgrade. Obviously it would help overall performance but is it absolutely necessary?
Beware the fps chasers - a smooth performance is always my priority. I would rather have a smooth 25fps than a stuttery 50.