How do I convince my team performance matters?
Stop arguing that it matters in general. Show what it costs here, on this page, this quarter.
Nobody disputes that performance matters in the abstract, which is exactly why the abstract argument never wins a sprint. The winning version is specific and local.
Tie one number to one outcome
“Our checkout takes 4.2 seconds on the median phone, and 18% of sessions leave before it finishes” is a business case. “The site is slow” is a complaint.
Then ask for one week, not a quarter. A visible win in a week buys the quarter.