Which Giant TCR bike would be faster and which is the better buy?

2021 Giant TCR Advanced 2 Road Bike

https://cyclelimited.com/products/2021-giant-tcr-advanced-2-road-bike-med-large-2

2015 Giant TCR Advanced SL 1 Road Bike
https://cyclelimited.com/products/2015-giant-tcr-advanced-sl-1-road-bike-med-large

Purpose would be for Ironman training and for raceday