Improve by itself doesn't imply a direction. It has to be inferred via context. Improving page load time by 500% is perfectly reasonable to say, the reader infe

Improve by itself doesn't imply a direction. It has to be inferred via context. Improving page load time by 500% is perfectly reasonable to say, the reader infers that improve means decrease in this case. Just as you can improve a golf score, or a marathon pace, or your BMI.