Thanks for the example. I tested the link and it's not slow for me. The first thing to try is a Forced Restart.
- Press and quickly release the Volume Up Button
- Press and quickly release the Volume Down Button
- Press and hold the Side Button until you see the Apple Logo
(Keep holding past the Power Off Slider which can take up to 30 seconds. If you see the Emergency SOS/Medical ID toggles, try again as you are performing it incorrectly.)
Then there are a few things to check.
- Settings > Battery > Battery Health. What percent is displayed?
- Settings > General > iPhone Storage. How much storage out of what are you occupying?
- Check how many Safari tabs you have open. Each one open takes a fixed piece of the RAM.