Basically the last real big jump in performance was SSD. I have used M1 - M3 Macbook at work. While they are faster it wasn't that much faster compared to the switch between HDD and SSD. Even On devices Voice Dictation and other AI features worked pretty well.
As many stated software is getting slower. Security and all the other requirement will likely put more burden on your machine. So there may be a need to upgrade this 2015 machine in the future, but as far as I am concern most of those have to do with Memory rather than CPU performance. I could have a 2015 Quad Core MacBook Pro and 32GB and I am sure it will last me till 2030.
ARM and Qualcomm have both catch up to Apple in CPU performance. Oryon and Cortex X725 is now within ~12% ( IIRC ) IPC difference or even similar if you ignore a small type of workload. With X730 and Oryon 2 both expect to eliminate or even exceed that gap. Unless A19 / M5 pull some other magic tricks we have basically make High CPU Performance a commodity.