At first check the performance with 3.3.3 latest snapshot. Also try to turn columns menu off.
But unfortunatelly we must admit that this community contributed component was optimized not much and most of optimization was targetted to 4.x.
Turning off the columns menu helps a bit, it reduce the size by 500 kb. But is not enough as the result page is still greater than 2.5 Mb
Many lines of JS are here to supports the columns D'n'D functionnality. Is it possible to turn off the D'n'D and still got columns resize one ?
Unfortunatelly such task present in jria but it not solved so you could not turn this off at component level. you could only patch the component on your own.