Ann: GBM Agile Update, page-175

The statement you are referring to is made in reference to recurrent GBM. The 15+ months demonstrated by paxalisib in the GBM Phase II study was in newly-diagnosed (unmethylated) patients. As far as I know, to date there is no data on how paxalisib performs in recurrent GBM.

The 15 months-mark is very specific to the indication and population.
Your view of "But the view of this high profile research is that 15 months in new or subsequent studies, is good enough." is too generalising.
Patients with newly-diagnosed methylated GBM already have a median OS of around 22 months. Achieving 15 months in this GBM population would be meaningless.

Lastly, let's assume paxalisib replicates the phase II results and demonstrates a median OS of 15-16 months in the newly-diagnosed, unmethylated population. If the TMZ control arm demonstrated the same results, chances for paxalisib's regulatory approval in this population would be very slim. In the end it will come down to the difference between both arms, not the absolute number.