Optimize our ReactJS app for faster loading speeds

We're looking for someone who can take a look at our reactJS app and optimize it for faster loading times. Currently the performance is rather bad in older devices especially, which is hurting the user happiness. We would like the app to get to a 90+ lighthouse score, and Gtmetrix score of A at least. This should be seen as a paid task for a senior developer. We are looking for someone to join us full time, so if you are able to handle this task, we'll hire you on a long term basis. Will happily provide link to app in PM, just message us. You may see this as a paid test task for an opening which we currently have, which is a full time (40hrs per week) senior reactJS position. If you do a good job and you get along well with our team, we'll hapily hire you for this position. This is why its preferrable if you're fully available currently.