If you can make pastry, make it from scratch it tastes so much better than bought.
For a simple shortcrust use half fat to flour, say 200g flour to 100g of butter and a good pinch of salt for taste. You can blitz it all in food processor if you have one or take your time to really combine the flour and butter till it looks like big breadcrumbs. You can enrich it with an egg yolk and then enough water to bind it all. Add your water slowly dont put it in all at once and you shouldn't need more than 60ml of water. Wrap it in clingfilm and leave to rest for 30mins in the fridge
It will need longer than 15mins.....normally about 30mins and dont forget to eggwash your pie before it goes in the oven