What to do with an old 401k

I have a 401k from a previous employer with about 30k. With my current job I have a 401k and other IRA options. I know I could roll the old one over but my hang up is, the old 401k dramatically outperforms my active 401k. I’m talking like 20+% a year for 15 years now. My actual money in was ~2k with the company matching ~1k.

Should I just leave it and let it continue to grow? Can I/should I directly contribute additional funds into it? Better options?