I have tried multiple possobilities, I don't think qsqltablemodel works for me. Though it load data directly from database, as you keep scrolling down it loads more and more data in table and hence the memory usage keep on increasing.
What I think will ideally work is being able to load set number of rows in model. As you scroll down it loads new rows but also at the same time unloads what's already there. So at any point of time we only have set number of rows loaded in model.