174 / 155 = 1.123 so 12% drift.
However, your drift at 155 was only 2%, so your actual AeT HR will be higher, and could easily be 160.
You can do as much of your training as possible at or below aerobic threshold. But when the AnT / AeT gap is less than 10%, then the exertion required in Zone 2 will be noticeably higher. Because it’s higher, it’s less sustainable, so then aerobic capacity work shifts to Zone 1.
For example, if your AeT is actual ~158 (10% below 174), then you can estimate the top of Zone 1 is ~142. Recovery workouts would be even lower, perhaps mid-120s.