The trouble is the game designer for HG2022 changed the rules, so within the setting the Imperium has had over 100 years to find out how to build TL15 warships according to those rules, they have even fought a short war with them.
In point of fact according to Mongoose Traveller rules the Imperium has had experimental TL15 technology since ~300.
But the rules do a lousy job of producing the setting as it existed before the rules changed.
So either the rules need to change to model the setting, or the setting elements, ie the warship designs, need to be brought in line with the rules.
Which means spinals are not worth any investment, imagine a 500,000t Tigress without its spinal but with 50 500t meson bays with very long range advantage and 50 500t particle bays with very high intensity...