So I found this cool article (somewhere) and will repost it here. It tells us whats available at TL15 within the Third Imperium, and how good (or not so good) it is as this tech level.
Stuff to remember at TL15:
+ Artificial Intelligence (AI) is "early production" at best. Closer to a Ford Model T than to a current model Ford Focus. Shipboard computers and other big systems "appear" smart but they are expert systems without real creativity. And AIs are often quirky (Think of the B5 AI that got "deactivated very quickly")
+ The nobility uses tech to impress. A floating palace (even more so if the world does NOT have gravtech) isn't all that uncommon nor is it "high tech" by imperial standards.
+ At TL10+ GravTech is everywhere. A modern Traveller city might look like a cross between "The Jetsons" and "5th Element" with three dimensional traffic grids. Or (for a bleaker view) like Earth in Pournelles CoDominion where the rich use Gravlimos (In the book they use helicopters) to move between work-enclaves and home-enclaves bypassing the slum zones in between
+ Energy is cheap. Any TL9+ planet can get all the energy it wants almost for free by putting a few solar satellites in orbit. Access to space is like taking a plane to America in the 1970s at that TL. At higher TLs it's "taking the tram"
+ No surprises. Tech is an incremental think with little jumps between TL9 and TL15. It gets more refined, more effective but remains the same.
+ Access to space is cheap. A 20dton Launch has the same cargo capacity to GEO as a Delta IV heavy but it's reuseabel with a turn-around time of hours, needs no special lauch pad (A concrete pad is IMHO recommended) and costs a measely 14 Million. And even the Air/Raft can (slowly) reach orbit if necessary. So basically every planet of TL9+ will have a huge orbital infrastructure (unless severe athmosphere conditions intervene) and lots of boats (some bigger than a players starship) running around in system.