1nzfe valve and valve springs

[tsu]

Not sure whether someone has asked for this matter. I have a Yaris NCP91 (Gen II, 5-door hatchback, 1.5 litre 1NZ-FE engine). Currently, I'm using stock valve springs and stock camshaft in the engine, and now the springs seem to be floating around 7000 rpm.
My friend told me that 1ZZ-FE valve springs can be a good subtitute for the stock valve springs. He said that the 1ZZ-FE valve springs are stiffer almost twice of the stock valve springs have.
I know that aftermarket valve springs would be a better choice, but since I'm still using stock camshaft, I'm afraid that aftermarket valve springs would be too harsh for the stock camshaft (the camshaft and its lobes cannot withstand the pressure from the aftermarket valve springs). Has anyone ever installed 1ZZ-FE valve springs into 1NZ-FE engine?. Any issues?.