If i was you
i would start something decent easy
Buy a slider.
Choose righ parts, try keep it very light weight.
https://www.ebay.com/itm/275419481649?hash=item402047c631:g:h3YAAOSwseFi9SN7
Lightly used X-MAXX
without electronics, body, wheels and so on.
These are called SLIDERS.
You need...
Yeah , you did say 15minutes runtime or more.
You need minium 8000mah then.
If you are fine with 5-8 minutes runtime only
then you can have smal 5000mah.
These we use only in light weight Buggies 1/8 normally to have about 10-12minutes runtime atleast.
Remember also that very light weight...
if you looking for 15min + run time there is no smaller than 8000mah then
Smal and light weight 8000mah 4s with great C rate are Gens -Ace -Bashing series.
What motor is 890kv ? 7200w ?
Leopard? Hobbystar ?
If you will drive 56 size motor and real 1/5 scale you want Max5 ESC 200a
Tell more...