You can learn to memorise cards (Even a full deck)
I often get a deck of cards shuffled, then dealt slowly into a face up pile in front of me. The spectator is asked to turn the cards back face down, and I proceed to name them all in order.
I can vary this, and ask them to name a card, and I will tell them what position it is in. Or name a position, and I tell them the card.
As this isn't magic as such, and there is no secret, I feel it is ok for me to explain my method here. If not, Mods, please remove the post!
I basically have a set journey in my mind. A 52 stage journey. For example, walking from my house into Chiang Mai City Centre, and to my favourite bar.
I split this into stages. Stage 1, at my front door, Stage2-Closing my front gate, Stage 3 - Passing my local grocery shop. etc etc
I then assign a person I know to each value of a card. So an Ace would be my best friend, 2 is my Mum, 3 is my Dad etc.
Finally, each of the suits, I assign a memorable action. So if its a Spade, the action would be hitting me on the head with a Spade. A Club could be walking upto me with Flowers in their ears, Hearts would be someone on their knees proposing marriage, etc etc.
So once I have all those things in my mind and memorised, I am set to go.
First card dealt in front of me for example is the 2 of hearts. So I imagine being at STage1 of my journey (My front door), and I meet my Mum (Number 2 person) who is on her knees proposing marriage. This image is easy to remember!
Next card is the Ace of spades, so I imagine being at my front gate where my Best friend smashes me on the head with a Spade.
Continue throughout your journey till the last card.
Now all you have to do is recollect the journey in your mind and translate it back to the various cards/positions etc.
15 cards would be easy. 15 step journey!
Practise, and you will find its quite easy. However, repeating the effect immediately can get a bit confusing!
Hope this helps
Phil