As bigt61 pointed out, you went over 7,000 miles in 3 months. I agree that if you continue that pattern of usage, you can easily do 10K miles.
I have found that if your pattern of driving changed to more stop and go, with shorter trips over a longer period of time, the TBN retention would not have been as good for the same number of miles.
I do believe Mobil 1 EP can last the advertised 15K miles, and even Amsoil can go 25K between changes, given the right conditions. Long highway trips, with lots of miles over a short period of time are pretty easy, especially with the Toyota engines.
Anyway, congrats on an excellent report.