Here's a simple, no programming suggestion.
For each LED, use a single open-drain version of the 74HC595 serial-in 8-bit-parallel out shift register. One open drain version is from NXP NPIC6C595-Q100.
The pulse will go into the SI (shift input).
All 15 shift registers are continuously clocked by a 8 Hz RC clock.. nothing accurate needed here.
The 8 open-drain outputs of each shift register are wire-or tied together, then to the led, then to a current limiting resister then to your +12V line.
The pulse will shift into the register, and appear at each output, for 8 pulses, sinking current through the LED for 1 second.
For fewer parts and a bit of programming effort, you use an MCU as others have said. But you need an MCU with 30 I/O's or use a few SPI port extenders, or use 2 eight bit shift registers to drive up to 16 LEDs (with timing in software), etc.