So ... I finally got to one point.
1) I used SmartBurn3.5.5 and all the ckecks were unchecked.
I used action "Clear OPC History" and voila ... I was able to make TRT @16x, in Nero CD DVD Speed 220.127.116.11
2) I repeated TRT tests with different written DVD+R discs and all is fine now.
But I still didn't understand why I had that behaviour.
3) I made a burn @8x, which I usually do for saving my data, on DVD+R Verbatim MCC 004. Again. I used Nero Burning ROM 2014. I had the same behaviour with Nero Burning ROM 10. After complete write, at verification phase it was again slowly.
I assumed is a bug in Nero.
4) I made the same write test in Nero CD DVD Speed 18.104.22.168. Wrote @8x, did not eject the disc, and immediately after that I made TRT test. Voila -- > read at 6x.
5) I ejected the disc and reintroduced in the unit. Made again TRT test. Now it was at 16x, as it should.
Conclusion: Problem is on iHBS312 firmware. If you select burn @8x (or maybe also 12X, or just smaller than 16x), the immediate read, without ejecting the disc, will be made at a lower speed, like 6x.
It is very annoying for me, because I use to make multiple burnings, in the same time, with multiple Nero instances and choose 8x as burn speed. I always use verify, so ... my iHBS 312 2 will be the last one for finishing all the process, because the verify is made at slow speed.