Better way to remap 16-Key Touch keypad
Is there any way to optimize this code:


Absolutely, yes. Don't use String for this, you are seriously wasting memory. Instead you can use a struct:

struct keymap {
    uint8_t code;
    const __FlashStringHelper *value;
};

const struct keymap keyRemap[] = {
    { 1, F("1") },
    { 2, F("2") },
    { 3, F("3") },
    { 5, F("4") },
    { 6, F("5") },
    { 7, F("6") },
    { 9, F("7") },
    { 10, F("8") },
    { 11, F("9") },
    { 14, F("0") },
    { 13, F("Clear") },
    { 15, F("Enter") },
    { 0, 0 }
};

void loop() {
    int Key = Read_Keypad();

    if (Key != 0) {
        lcd.clear();
        lcd.setCursor(0, 0);

        for (int x = 0; keyRemap[x].code != 0; x++) {
            if (Key == keyRemap[x].code) {
                lcd.print(keyRemap[x].value);
            }
        }

        delay(160);
    }
}