Counting 0..15 in each cell (using 15 cells) would be quite foolish.

You get the disadvantage that it takes extra code to display in decimal. But you don't really save any memory.

Either go for binary counting, using 3 memory cells with 0..255, or use decimal counting, where you have 6 memory cells with values 0..9.

But you still haven't said what frequency your pulses comes in with. That - and the quota between high/low - will affect how much time you have for detecting a pulse. This is very important if you are going to poll a processor pin, since the time you spend converting and emitting to the display is time when you are too busy to poll the pin...

But if you really want to learn - why not learn to use a pin interrupt or the timer/counter hardware?

And why do you not learn how to perform a shift/add conversion from binary to decimal? Is the goal to learn, or to just manage to get something that count pulses but doesn't work well (such as displaying hexadecimal data on the display)?