Early last year, venture capital firm Felix Capital set out to raise $600 million for its next fund, touting previous investments in fitness-machine maker Peloton Interactive Inc. and food-delivery service Deliveroo. But investors want to see returns from older funds before they commit new capital, and Felix is still $150 million short of its target, according to a person with knowledge of the matter.It’s emblematic of broader struggles across venture capital. Fund investors, known as limited pa...