We expected the Payment page to render much earlier than it is. According to SpeedCurve, it's still much slower than what we expected. This ticket is to do further investigation and understand what the underlying problem could be.
Some ideas were to:
Look at caching on CloudFlare.
Remove Optimizely and Segment to see what difference that makes.
Here are some links:
On SpeedCurve: Favorites > Basket Comparison. We have best case (chrome/US) followed by worst case (samsung/India). We also have direct (no SSO to ecommerce included) followed by charts that include SSO + Add Product time.