Need help, Why is this code running much slower than Uno?

#define ledPin 3
#define numLeds 24

// Define the array of leds
CRGB led_array[numLeds];

LiquidCrystal_I2C lcd(0x3F, 20, 4);

const int HomeBTN = 13; /// pin connected to button

int MPH = 0; // to be replaced by a MPH calculator in loop connected to bike
int OldMPH = 0;
int differ = 0;

// The step angle is 5.625/64 and the
// operating Frequency is 100pps. Current draw is 92mA.
////////////////////////////////////////////////
//4096
// 2.25 deg per MPH, 5.625/64 = 0.0879, 2.25/0.0879 = 25.6 steps per mph

///////////////////////////////////////////////////////////////////////////////
/////// Stepper Settings /////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
#define StepsPerRev 2080 //2080 seems to be cloest non float figure //37.9 //88641975 /// 2037.88641975 /// 2048 /// 4075.7728395
#define mphRange 80 // dial range for MPH
#define StepsPerMPH ((StepsPerRev) / 2 / (mphRange)) //13
#define speed 15 //500 at 5v 700-750 at 9v some skipping 850 at 12v but too hot i think
//////////Stepper Call
newStepper mph_stepper(StepsPerRev, 8, 9, 10, 11); /// 64 steps per motor 360 (not geared rev)
///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////
void updateMPHled (int cMPH)
{
int light = ((numLeds + .0f) / (mphRange + .0f) * cMPH); // (numLeds / mphRange * cMPH);
//Serial.print("Blah " + String(light));
//Serial.println();

for (int led = 0; led < numLeds; led++)
{
int cVal = 0;
if (led <= light)
{
cVal = 5;
}

led_array[led].setRGB(cVal,cVal,cVal);
FastLED.show();
}

}

//////////////////////////////////////////////////////////////////////////////
void moveMPH(int inMPH) ///function to move motor to the mph detected and displays information on the screen
{
// MPH = inMPH;

//lcd.clear();
//lcd.setCursor(0, 0);
//lcd.print (String("MPH= ") + inMPH);
//lcd.setCursor(0, 1);
//lcd.print (String("Old MPH= ") + OldMPH);
//lcd.setCursor(0, 2);
//lcd.print (String("Difference= ") + (inMPH - OldMPH));

//Serial.print(OldMPH - inMPH);
//Serial.println();

/// will need changing for interrupted calls for faster mph updating. Will need a seporate var holding current mph or step count possision

if (OldMPH < inMPH)
{
for (int i = 0; i < (inMPH - OldMPH); i++)
{
mph_stepper.step(-StepsPerMPH);
updateMPHled((inMPH)); // StepsPerMPH) + (OldMPH / StepsPerMPH) );
}
}
else
{
for (int i = 0; i < (OldMPH - inMPH); i++)
{
mph_stepper.step(StepsPerMPH);
updateMPHled((inMPH)); // StepsPerMPH) + (OldMPH / StepsPerMPH) );
}
}
OldMPH = inMPH;
}

/////////////////////////////////////////////////////////////////////////
void ZeroHome()
{
while (digitalRead(HomeBTN)== HIGH)
{
mph_stepper.step(11);
}
OldMPH = 0;
}

////////////////////////////////////////////////////////////////////////
void setup()
{
mph_stepper.setSpeed(speed);

FastLED.addLeds<NEOPIXEL,ledPin>(led_array,numLeds);
pinMode(HomeBTN, INPUT_PULLUP);

//Serial.begin(9600); /// for serial feedback

/// setting up LCD during testing
//lcd.begin ();
//lcd.backlight();
//lcd.clear();

/// Current starting demo/homing code, to be replaced with reed detection at 0 and led demos.

ZeroHome();

//for (int i = 0; i < (mphRange / 10) + 1; i++)
//{
// moveMPH(i * 10);
// //delay(200);
//}

//delay(1000);

//for (int i = (mphRange / 10) ; i >= 1; i--)
//{
// moveMPH(i * 10);
// //delay(200);
//}

// ZeroHome();
// delay(1000);
}

//////////////////////////////////////////////////////////////////////////////
void loop() {

//lcd.setCursor(0, 3);
//lcd.print (String(digitalRead(HomeBTN)));
//MPH = random(0, mphRange + 1); // to be replaced by code that calculates MPH

// if (MPH < 0)
// {
// ZeroHome();
// }
// else
// {
// moveMPH(MPH);
// }
moveMPH(0);
delay(100);
moveMPH(80);
delay(100);
}