how to find the noise frequency in ECG signal?

I perform the fft, but I still don't know which frequency is the noise except 1200 Hz. I also want to flter the noise using FIR filter. The lecturer said

there are three noise frequency.

I also want to confirm is it right that the 15 Hz is the main frequecny of the ECG signal?

Your help would be highly appreciated.

clear
load('coursework2ECG2022.mat')
plot(t,signalNoise1)

T=Ts;
Fs=fs;
L=size(t,2);
X=signalNoise1;
X = X - mean(X);
%FFT
Y = fft(X);
P2 = abs(Y/L);
P1 = P2(1:L/2+1);
P1(2:end-1) = 2*P1(2:end-1);
f = Fs*(0:(L/2))/L;
figure;plot(f,P1) 
title('Single-Sided Amplitude Spectrum of X(t)')
xlabel('f (Hz)')
ylabel('|P1(f)|')