Need some lipo size help here

Back to this guys

I know you all as low KV, and high voltage, which I want to do, but cant choose here

Do you guys thing a TrueRC 1500MAH 3s 15C pack is enough for my application, or no? I want max performance, with a small size, a 25C high mah thunderpower pack that is tiny is 75 bucks...

A normal 6c pack is 102mm, by 30

I need it small as possible to fit my RX on the batt side so I dont have to stack the electronics on one side...

So Can anyone help me find atleast a 20C pack over 1000mah? under, or close to 85 x 31 x 18mm that doesnt cost a ton of money? 40 bucks for a little lipo is on the high side IMO

Thanks