How to calculate how much high ESR capacitance to smooth impedance spikes?
For a SMPS 3.7 to 5V, 15A   your load is 5V/15A= 333 mΩ 

For ripple to be  1% of 5V or +/-50mV  your bulk cap ESR must be 3.3mΩ 

Typically you can expect ESR*C &lt;=10us for low ESR and > 100us for general purpose e-caps in this size range.   

Thus using above Rule of Thumb for cheap low ESR,  T = ESR * C = 10us = 100uF * ESR , thus ESR= 100 mΩ   Therefore you might need 33 Caps or get 25 Caps with ESR &lt; 25/33*10 = 7.5mΩ
If you want &lt; 1% ripple then go for the best ultra-low ESR e-caps T=&lt;2us 

There is a matter of size and rms ripple current rating at some temp rise and MTBF at rated temperature.  You want to use at least 25% derated values.  So with 15Adc rms ripple current, est. the ratings will be shared by 25 caps or ~ 1Arms min rating per cap. 

You may want to consider 1uF caps as well.

Examine the RLC parts as a Low Pass filter and examine the Q and harmonic rejection.
 

Inductor peak currents may be 35A also of concern.  

Phase lag of LPF reduces phase margin of loop filter step response.

Arrange for lowest inductance.

update

Simulation to validate assumptions previously stated

Just a quick &amp; dirty  simulation of a SMPS with a slider for ESR.

Bottom Line
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If you are skilled in understand Q , impedance matching of RLC and the effects of phase shift on feedback of 2nd order filters, you will realize these are not compatible properties. The 180 deg phase shift of an RLC filter interferes with the step response stability of a closed loop voltage regulator unless you use feed forward compensation, Current feedback in  addition to voltage ratio feedback or error to Vref ( here simulated crudely with a Zener).

Thus ripple noise is unavoidable inside the closed loop 2nd order loop.  However ripple filtering you do outside the loop has no effect on stability.If I could demonstrate this, I would show ESR going to uOhms with ripple reducing meanwhile Q has risen >>1 and caused phase margin to drop very low and disturbances to load cause incredibly bad over/undershoot at the loop filter peak resonance frequency.


Thus too low ESR results in low phase margin and instability but low ripple.   Expect to need phase lead compensation with ESR+LC filter Q near 1.