ST7735 at high rate?

  var spi = new SPI();
  spi.setup({mosi:B15 /* sda */, sck:B13 /* scl */});

You could use hardware SPI and set higher speed?

Also you could try to enable JIT compiler in the flip() method
https://www.espruino.com/modules/ST7735.­js
but that may not help that much.

Also there is the relatively generic lcd_spi driver
https://github.com/espruino/Espruino/blo­b/master/libs/graphics/lcd_spilcd.c
that could maybe work with ST7735