Thank you for your request.
We only have the GA monthly travelcard, valid for 1 month. Unfortunately, we don’t have a GA for 10 or 15 days. You could also take super saver tickets or saver day passes. We recommend to buy the saver offers in advance to get cheaper offers: Super saver offers.
If you decide to buy individual tickets (also supersaver offers) then the half fare card can also be worth it. It is basically amortized with a few trips, even if it is valid for a year.
Have a lovely day.