I believe the difference you see in pricing was due to the fact that in 2014, Giant produced 3 different carbon frame layups, Advanced SL, Advanced and the base composite grade. So in 2014, the TCR Advanced used the mid grade weave (Advanced) while the entry level TCR Composite used the base composite weave. In 2015, Giant eliminated the base composite grade and just used the Advanced weave for all carbon TCRs, except the TCR Advanced SL, which still used the top Advanced SL weave. So in 2015 and newer, the three lines are Advanced SL, Advanced Pro and Advanced. The 2014 Advanced would compare more along to the lines of the modern Advanced Pro in terms of the TCR tiering.
Anyways, long story short, don't look at the MSRP to make your decision and don't put too much weight into what model year the TCR fell into in terms of the three spec lines. Both models you are looking at are pretty comparable and your choice should be based upon mainly if you like SRAM vs Shimano. But you're comparing what was the mid tier TCR in 2014 to what is now the base model TCR in 2015-2016. I believe in 2016, the TCR also has thinner seat stays, which is supposed to make it more comfortable.