Is 55ns SRAM fast enough to drive low resolution VGA?
$$ {1 \over 55 \text{ ns} } = 18 \text{ MHz}.$$

640x480 @ 60 Hz VGA uses a pixel clock of 25.175 MHz, so there's no way you can drive that from a 55 ns SRAM. If you can't find a large enough 15 ns SRAM, you can group a couple of them together with an address decoder.